Yeah, I'll believe that when I see it. Stores will just change the price of everything except stuff that falls on exactly .00. Things that are .01, .02, .03, and .04 will all be rounded up to .05. It's not like companies are, as a whole, going to just say, "Sure, let's just take a tiny loss here and make up for it with a tiny gain here." They'll just take a tiny gain everywhere.
Main reason why I'm against getting rid of the American penny, actually. Sure, it costs more to make then its worth, but we're still talking about a comparatively tiny amount when put next to the overall federal budget and, dollars to rounded up nickles, I'd bet that the combined cost on consumers for everything they buy being rounded up, even if only by a cent or two each, will in the long-run end up increasing the cost of goods and services by more than the net loss of making pennies ever was.
Problem with your theory is, it doesn't exactly work like that. They can't just raise the price on a certain good and get it so it's in the round up column, different combinations will always add up different, and then you factor in taxes. Stores might increase the prices a bit to try and make up for any potential loss, but prices do go up(and it wouldn't be substantial) and there's not much else they can do otherwise.
Plus, obviously, this doesn't affect debit purchases whatsoever, which I would imagine are the majority now. All in all, this is probably pretty likely a non-factor.