Remember when Chipotle got in trouble for rounding 24¢ and 26¢ to 25¢, to save time making change? [1] It was not unfair on average, and it surely sped things up, but they stopped because it's technically not correct.
I can see if being considered unfair if it's a single business, but I do think that it's at least a little funny, considering we have penny rounding (to the nearest nickel) here in Canada since geting rid of the penny. Now it's by default, everywhere. And as someone that uses cash for all in-person purchases, it's actually really, really nice