This isn't possible due to rounding. If you live somewhere with 7.5% sales tax (just to pick a number) and you want an item to be exactly $1.50, you have to price it at $1.40. Want five of those? The total comes to $7.52.
In Canada (and the US?) that's what happens with gasoline, but not with anything else. I think that's strange.
Honestly, even if this is only done for the "critical path", it can still make life easier. I pay $4.16 for a large latte at Starbucks. It would be easier if it was $4 or $5. I don't care if the price is easy for two lattes or if I get a half-caf skim extra hot latte with 94 extra espresso shots. Just make the basics simple, and you will save a lot of effort.
(Profile, then fix the slow parts.)
I always find it frustrating when I visit the US dealing with pre-tax price stickers. Thank you Oregon for not doing this. :)
Fenway Park and Gillette Stadium show post-tax prices.