Anything measured by weight is already rounding prices to the nearest cent. If something is $1/lb and I have 0.995 lbs of it, I get charged $1.00 not 99.5 cents. Presumably just rounding to the nearest 5 cents isn't that different.
Of course we don't expect anyone to be charged fractional cents because our currency doesn't support it. So just changing our smallest currency unit from 1 cent to 5 cents.
