It is something that has evolved over time. Back in the day, when a penny had worth and money was rather scarce, the price of gasoline flucuated in values less than one cent. As time went on, the market held on to that variation though the value of a penny became less and less. That fractionalizing probably came from the wholesale level and the retailer simply tacked it on to the price so that the retrieval at the retail level was in whole cents. Now, it is more of a market ploy that allows more money to be collected while appearing to sound cheaper...like getting a lunch for $9.95 as opposed to $10. Collectively, over time, that 9/10 cent amounts to considerably more money in the pocket of the seller.