Taxation in stores

Imagine that you are out shopping with a certain amount of money, say 20 bucks, and you find something that you really want, which is only 19.99 and you think "yesss, I can get that", but NO.... When coming to the counter,they would say that the price is around 21 dollars. In the United States, the final price is set at the counter when the tax has been added. The tax for groceries, clothes and most of the things you can buy in shops are usually 5%, which means that you would have to add 50 cents for every 10 dollar a thing costs. This can be a pain in the ass when you are out shopping, but luckily the tax is not as high as it is in Norway(25%), so it does not make much difference.