Whichever one(s) they wanted to deal with.
Presuming they set themselves up to accept each one, sure. There's nothing about any particular form of crypto that precludes accepting any other.
Nothing would stop a store from doing so, other than having to track a different price for every item in every kind of crypto. I can't imagine anyone would want to do that, just because of what a PITA it would be.
Congrats, you have successfully pointed out the reasons most cryptocurrencies are not very good at being currencies. It's all the downsides of paying for things with precisely weighed flakes of precious metals, but with a massive energy cost to make sure you aren't trying to give the same silver shavings to two different people.
Now, there are things called "stable coins" that solve some of those problems, which are "stable" because they explicitly peg their price to some fiat currency so that price fluctuations are less of a concern (they're as much a concern as using the fiat currency in question in general).