Sales tax is the compliance area where local businesses most often discover a five-figure problem years after it started. The rules are not conceptually hard, but they are administered by thousands of separate jurisdictions with different rates, rules, and calendars. Here is the working version an owner actually needs.
Nexus: where you owe
Nexus is the connection that obligates you to collect. A physical location creates it in that state instantly — no minimum sales, no waiting period. That means a single storefront registers in its home state before the first transaction, full stop.
The second kind is economic nexus, and it is where local businesses get surprised. Once you ship, deliver, or provide taxable services into another state above that state's threshold, you can owe there too. A hundred thousand dollars of sales into a state is the most common threshold, though several large states set theirs higher and a few still count transactions as well as dollars. A shop that starts shipping online, a caterer working across a state line, and a contractor taking jobs one county over have all crossed into this territory without noticing.
If you sell through a marketplace — a major online platform, or a food delivery app — the platform is generally required to collect and remit sales tax on those orders as the marketplace facilitator. You still report the sales, but you do not collect the tax twice. Recording those orders as if you owed the tax is a common and expensive bookkeeping error.
Rates: which number to charge
Your rate is rarely just the state rate. It is the state rate plus county, city, and any special district that overlaps that address, which is why two shops on opposite sides of the same street can charge different amounts. Two sourcing rules decide which address governs.
- Destination sourcing — the rate is based on where the customer takes possession. This is the majority rule, and the one that applies to deliveries.
- Origin sourcing — the rate is based on your location. A minority of states use this for sales within the state, which simplifies life considerably if you are in one of them.
- Product rules override both — groceries, prepared food, clothing, and prescriptions are taxed differently by state, and prepared food often carries an extra local rate.
- Services are taxable in more states than owners expect. A few states tax most services outright; many others tax specific ones such as repair, installation, or landscaping.
- Delivery and shipping charges are taxable in a large number of states when the goods themselves are taxable.
Use your state's address-based rate lookup rather than a ZIP code table. ZIP codes cross jurisdiction lines, and rate errors compound quietly across thousands of small transactions until an audit adds them up.
Filing: how often, and the zero return trap
Your state assigns a filing frequency when you register — monthly, quarterly, or annually — based on expected volume, and it can change as you grow. Two rules matter more than the calendar itself. First, you must file for every assigned period even when you collected nothing; a missed zero return generates a penalty and, repeated, a revoked permit. Second, many states offer a small vendor discount for filing and paying on time, which quietly pays for part of the compliance work.
Sales tax you collected is not revenue and was never yours. Treat it like money you are holding for someone else, because legally, that is exactly what it is.
Exemption and resale certificates
When you sell to a reseller, a nonprofit, or another exempt buyer, the exemption is only as good as the certificate in your file. Collect it at the time of the sale, check that it is complete and current, and store it where you can produce it years later. In an audit, an untaxed sale without a valid certificate becomes a taxable sale, and the tax comes out of your pocket rather than the customer's.
The same works in reverse when you buy. Goods you will resell can be purchased tax-free with your own resale certificate, but supplies you consume in the business generally cannot. Retail and service businesses that stock both — a salon buying both retail shampoo and back-bar product is the classic case, covered in the salon and retail guide — need to split those purchases correctly at the point of purchase.
Industry rules that override the general ones
- Restaurants — prepared food is taxed differently from grocery items, often at a higher combined local rate, and comps and employee meals have their own treatment. See restaurant accounting.
- Contractors — many states treat contractors as the consumer of materials, meaning you pay tax on purchase and do not charge the customer, while others distinguish lump-sum from time-and-materials contracts. Getting this backwards is the most common trade audit finding, covered in the contractor guide.
- Retail with services — repair labor bundled with a taxable part is treated differently from standalone labor in most states.
If you are already behind
Unfiled periods do not age out, and interest runs the whole time. The good news is that states would rather have compliant taxpayers than perfect ones, and most offer a voluntary disclosure agreement: you come forward before they contact you, they typically limit the lookback period and waive some or all penalties, and you file and pay for that window. That option generally disappears the moment a state contacts you first.
- 1Establish where you actually have nexus today, physical and economic, before doing anything else.
- 2Quantify the exposure by period and state, so you know the size of the problem rather than fearing it.
- 3Approach the states through voluntary disclosure where the exposure is meaningful and you are not yet under audit.
- 4Register, file the covered periods, and put a filing calendar in place so it never recurs.
If that sounds like your situation, sales tax compliance is a service we scope as a fixed fee — nexus study first, so you get the size of the problem before you commit to fixing it. Clean books make it far faster, which is one more argument for monthly bookkeeping and for bringing in help before the notice arrives. For the wider compliance picture, start with the local business accounting guide. This article is general information, not tax advice for your specific situation.