Sales tax is not part of your income and not an expense. It is money a customer pays that you hold for the state and send along on a schedule. Treating it as your own revenue is how businesses find themselves unable to pay it.
When you have to collect it
You generally must collect sales tax when you sell taxable goods or services in a state where you have a connection to that state, called nexus. Having a store, an employee or inventory in a state creates nexus. Since the Supreme Court’s 2018 Wayfair decision, so can selling enough into a state remotely, and many states use an economic threshold for this that varies by state.
What is taxable varies
Each state decides what it taxes. Most tax tangible goods, some tax certain services, and many exempt categories such as groceries. New Jersey’s general rate, for example, is 6.625%, with categories such as most clothing exempt. Rates and rules change, so check the state before assuming.
Register first, then collect
You register with the state’s tax agency before collecting, and the state assigns your filing frequency, commonly monthly, quarterly or annually. Returns are usually due even in a period with no sales.
Exemptions and resale certificates
Some sales are not taxable, for example sales for resale or to exempt organizations, but only if you hold the right certificate from the buyer. Without it, the state can hold you responsible for the tax.
Selling through a marketplace
Many marketplaces now collect and remit sales tax on the sales made through them. Your own direct sales are still yours to handle.