Sales tax is calculated using a relatively straightforward formula. Take the price of the item, and multiply it by the percentage of sales tax being levied.
For example, suppose that an item costs 20 dollars and there is a six percent state sales tax. Multiplying 20 by .06 yields 1.2. This means that the state sales tax for that item is $1.20. To get the final price of the item, add that number to the original price. In this case, the final price for that item would be $21.20. Several websites also offer calculators which figure the tax for the user.