If its a wide region ad (can even be just across a metro area) showcasing a price then yes, they wouldn't know the price at a given store because the tax rates can change in less than a kilometer.

If there's a TV ad for a medium pizza for $10 at a chain they can't possibly know the tax rates for whatever actual store I'm going to go order from.

And the listing on a website won't know until I actually put in my shipping information.

I doubt that most people in the US know the local sales tax. Let alone any change that may occur due to laws changing or traveling. I'd like to see the out the door price listed but that throws the 99 cent game off retailers like. Also I don't shop very often but Aldi US is the only place I've seen the eink price displays, the rest still have paper.