If someone is buying a banana for resale, or buying with WIC or SNAP benefits (among other things), they would not owe sales tax. So if the price included sales tax, the sticker price would not be the final price.

You do not know the final price until you know how they are paying for it, what they are using it for, and when they are buying it (among other things).

Falsehoods programmers believe about sales tax (among other things).