I've lived in the states for 15 years now. I know roughly what to add, though I have to play guessing games depending on even the town that I'm shopping in, (quite literally I can even walk to two stores in neighbouring cities within range of my house, and pay different prices for the same goods).
It makes it no less absurd that I have to know and guess what the actual out of pocket expense is, no matter which way you slice it. Especially because it doesn't have to be this way. Given individual items aren't shown with their particular taxes on them, it obscures what I'm actually paying for what, until I've spent enough time shopping in whichever place I'm in to finally figure it out.
It's just one of many little ways that the US operates that's profoundly at odds with a positive experience for citizens. You _could_ have the prices right there in the stores. You _could_ structure your tax system such that the prices can actually be done that way and you don't get the rounding fun that you see mentioned elsewhere in this thread. However, because you do this "hide the actual price" there's zero incentive to actually implement tax approaches that are nicer as a citizen/consumer.
If you'll forgive a slight diversion, it's a similar deal with tax incentives. In a lot of countries around the world, they structure it such that the tax incentives happen at time of purchase, so e.g. a $2,500 rebate would result in you, as the buyer, buying at price $2,500 less than it would have been otherwise. You never see that $2,500 at all, you just see a much cheaper sticker price. It's end user focused, like you'd think a government for the citizens, by the citizens, would be.
The US approaches it such that you have to actually have the money spare up front, to eventually get it back (or mess about with your monthly withholding to try to claw it back that way, quicker). This penalises poorer citizens, who otherwise might have been able to afford to buy whatever thing it is that they could potentially afford. You essentially miss out on the tax incentives the government comes up with, unless you happen to be rich enough to afford a well versed tax accountant, or have enough luxury of time to sit there and work through all the possible rebates you might be eligible for. Neither of which poor or disadvantaged people tend to have.
With this being the way that tax incentives have long been done, there's no real incentive to try to do it any other way, even though it would be better for literally every citizen, rich and poor alike, with the possible exception of tax accountants. You'd all get specific rebates you were entitled for.