The quickest way to calculate sales tax is to take the sales tax rate in an area and multiply it by the dollar amount of the goods or services subject to the tax. For example, if there is a 6 percent sales tax on all purchases and a purchase is $200, multiplying 6 percent by $200 gives a result of $12.
Sometimes an area has a state tax and a local tax that have to be calculated. If a purchase is $100, the state tax is 5 percent and the local tax is 1 percent, $100 multiplied by 5 percent is $5, and $100 multiplied by 1 percent is $1. The two figures are added together for a total sales tax of $6.