For me, living in Texas, I would assume the final price is 10% more than the sticker price calculation. When I was buying groceries, this generally meant I was always "under" my estimate because most food isn't taxable in Texas. But I was never surprised by the final total at the register. At restaurants I assumed 20-25% depending on what the numbers were.

Now that I live in Europe, I don't even notice. They tell me the total, I pay. End of story.