The sales price can change at each store location. It would be even easier to put the full price on the item in the aisle. Stores now know their inventory and track it by the minute.

I've always thought that it's probably done to engender anger at the notion of sales taxes by making the difference much clearer than it is in other places where the prices are typically bundled, and to display a lower price than the consumer is expected to pay.

Not displaying the taxes is infuriating when visiting other places, since unless you look up all of the applicable taxes you're effectively just guessing at the cost of anything.

I think originally there may have been some "grumble why do we have to charge" but I feel much of it now is big stores wanting to advertise one price for the whole country as best they can - and "tax licensing and dock fees" is a way to get around the varying prices.