Article: No matter what the actual tax rate is, this will make your multiplication much simpler. The goal in estimating sales tax is to make the math simple enough to do in your head.  Don't bother with exact amounts, just estimate well enough to make sure you have enough money to pay for what you want to buy.  By using an estimate of 10% it will mean that, in most cases, you are rounding up, making your estimate more than you will actually pay. If you are actually rounding the tax rate down, make sure to remember that your estimate will be a little bit less than you will need to pay. This will give you a good, quick estimate of how much tax you will be charged. No need for complicated calculations, just move the decimal over and that will give you 10% of the cost on the tag. In doing this, you are actually multiplying the cost of your item by the decimal equivalent of 10%, which is obviously really easy! For example, .10 times $20 equals $2. Because we rounded up, your estimate will probably be higher than the tax actually charged, but you will know you can afford to pay the total cost. To use our example from the previous step one more time, $20 plus $2 makes the estimated total cost including tax $22.

What is a summary?
Round the sales tax rate to 10%. Move the decimal point in the cost of your item one space to the left. Add the estimated tax to the cost of the item.