I don't think a quarter is too far to round. The only kind of situation where it seems like it would be a problem is like the rare time when you only need to buy one screw or washer or something.
*Edit* - As for the gas thing, yeah that seems kind of shady, since it's only reasonable purpose is to make the price look 1c lower. Constitutionally speaking I think that's a lot more squarely under the commerce clause than a lot of the other things they use it for, so I wouldn't see a problem with the feds regulating it. Not that I necessarily think they should, just that I don't think it would be a constitutional issue.