When you say "people" you're really talking about the stores, right? The stores just put the price they charge, not the taxes which they don't get. Yes, taxes vary from state to state, but it's not like we're all going to different states every day. I know what the tax rate is in my area, and so I know to add that when I see a price in a store.
If you really mean "people" as in customers, it depends. If I'm telling someone that a store has a good price, I'll just quote the store's price. But sometimes when I'm talking about what I paid, I'll include everything "Wow, I can't believe this cart of groceries was $150..."