\" \" Fractions abound in U.S. gas prices, thanks to a 1932 tax that never expired. The practice of tacking 9/10 of a cent on the end of a gas price goes back to when gas cost only pennies per gallon and was a tax imposed by state and federal governments. Gas stations added the fraction of a cent on the end of the price instead of rounding up the price. Today, U.S. gas prices tend to fluctuate between two and three bucks a gallon. Gas prices benefit from the same phenomenon, except on an even smaller scale, fractions of a penny instead of fractions of a dollar.