Does the average american, when naming a price of any given item, takes into account taxes or disregards it?

Watching a documentary, there was aremark from the journalist on how, due to how wildly taxation on goods may vary, from area to area, in the US, most retailers do not put the full prices on the shelves and instead just tally it at checkout.

This made no sense to me, a european, as when I go to any regular shop, prices already include all taxes applicable to the product.

There are specialty stores where VAT and other taxes may not be applied on the price on the shelf but those are usually wholesellers, selling for professionals, that already know what additional taxes will be added and at which rates, at checkout.

Not having the full price you'll be paying, on display, seems very underhanded and a bad practice. The client should know how much they are going to pay from the moment they pick an item.