Back in the day, gasoline was something like 9.3 cents per gallon. Then it went up to 9.4 cents per gallon and everybody freaked. You know the drill.
Anyhow, since traditionally there was always a fractional value attached to the price of gas, it just stuck. Pumps could easily pump for $1.93.5 instead of $1.92.9, but since they have the decimal place there they just put it as high as possible (to get as much money as you from possible).
It's kinda the same way that a new couch will cost you $999 instead of $1,000- essentially the same price, but one seems less than the other.
I've heard that gas pumps don't use the common sense rule for rounding the fraction. I don't remember the arcane method they use, but it works out to rounding up 2/3 the time instead of 1/2. It was on a site discussing the advantage of using temp-adjusted gas price for the consumer, which I can't find at the moment.
they've been temp. adjusted ever since i can remember up here in canada. maybe its because our climate goes to both extremes every year. there's a sticker on all pumps that says something like 'volume corrected to 15?C'
quite frankly i'm shocked if this doesnt exist elsewhere in the world