Sales tax makes up about 25 percent of state and local government revenues, according to the U.S. Census Bureau. When you buy an item, merchants add a certain percentage of the item's price to pay for the sales tax. You can quickly calculate how much money you will have to pay using a calculator. To perform this calculation, you need to know the price of the item and the sales tax percentage for your area.

Find out the total sales tax percentage in your area. In some areas, you may have to pay a local sales tax as well as a state sales tax. For example, if the state sales tax equals 4 percent and the local sales tax equals 1.5 percent, the total sales tax would be 5.5 percent.

Divide the sales tax percentage by 100 to convert it from a percentage to a decimal. For example, if the sales tax percentage is 5.5 percent, use the calculator to divide 5.5 by 100 to get 0.055.

Add 1 to the sales tax expressed as a decimal from step 2. For example, if you had 0.055, you would add 1 to get 1.055.

Multiply the result from step 3 by the price of the item to add the tax to the price of the item. For example, if an item's listed price without tax is $34, you would multiply $34 by 1.055 to find that the total price with tax added would be $35.87.

#### TL;DR (Too Long; Didn't Read)

Make sure that you account for all sales taxes when calculating the total sales tax in step 1.