[thereddaikon]

In the US, sales tax is handled on the state level not the national level. So it varies wildly.

[bialpio]

To expand on that: it's on state, county, and city level - I believe all those jurisdictions can introduce a sales tax.

[afiori]

the store is able to compute it on the fly at the register, so they can also print price stickers* (for products that don't have the price on them)

showing prices without vat should be banned for sales that are never business-to-business.

* unless they also vary wildly by the week