I think, since everyone basically ignores the .9¢/Gal at the end of gasoline prices, the gas stations are playing a mind game in which they charge a practically-unadvertized extra 10 to 20 cents on a full tank of gas. Fractional cents per gallon may have made sense when the price was well under $1/Gal, but these days it's just taking advantage of people. To remedy this, gasoline prices should be required to have no more than 3 significant figures.
If a sign displaying a gasoline price is only capable of displaying a price ending with a 9/10¢, that part of the sign should be disabled or covered. Alternatively, if the actual price is a whole number of cents per gallon, but the sign displays that price plus 9/10¢, this should be considered an allowable discrepancy, as it favors the consumer.
If fuel prices drop such that they are again under $1/Gal, or are sold by a smaller volume unit such as the Liter which is priced less than $1, then prices may include tenths of cents, as that would only be three significant figures. On the other hand, if prices continue to rise and surpass $10/Gal, then the limitation of three significant figures would mean prices must end in a multiple of 10¢.