How sales tax is calculated
To remove tax from a total, divide; don't subtract the percentage. Taking 8.25% off $108.25 gives $99.32, which is wrong. Dividing $108.25 by 1.0825 gives the correct $100.00.
Worked example
A $250 purchase at an 8.25% rate carries $20.63 of tax (8.25% of $250 is $20.625, rounded to the cent), for a total of $270.63.
How U.S. sales tax works
There's no national sales tax in the United States. Each state sets its own rate, and counties and cities often add local rates on top, so the rate you pay depends on where the sale happens. Five states have no statewide sales tax: Alaska, Delaware, Montana, New Hampshire and Oregon, though some Alaska towns charge a local one.
What's taxed varies too. Many states tax groceries at a lower rate or not at all, and some exempt clothing or prescription drugs. Your state's department of revenue publishes current rates and lookup tools by address.