Heh, heh....you might be interested in knowing that historically, that's because of you guys. (Or so I've heard, anyway....)

In the days of the colonies, the British put tax on several items (and, I think, imposed a sales tax.) When the colonies began their rebellions, people refused to pay the taxes any more. Shopkeepers who wanted to stay on the colonists' good side, while not having to stand up to the British, would add the tax into the price, so that people would pay British taxes without realizing they were doing so.

These days, it's illegal to disguise a tax by adding it automatically to an item's price or making it appear as if there are no taxes being payed on a taxed item. (Unless you're the US government and want to tax cigarettes or something.)