If you don’t need to work with the value, store it in a string. If you do, use a proper decimal type. (Your question may then apply to the internals of the decimal type, but the point is that that should be transparent to the developer accessing the decimal value.)
Meh, from what I've seen so far, it's just so people see, e.g. 2.55 $/gal with the tiny nine in the corner, stop by and get charged 2.559 $/gal (essentially squeezing that last cent out of customers.)
I'd be interested to hear if anyone else has seen any digit other than nine in the tenth-of-a-cent column though.
I believe it's because gas prices are quoted with tax (which is unusual in the US), and there is a federal tax ending in 9 tenths of a cent. Probably lobbied by the small 9 marquee digit manufacturers of america.
Australian fuel prices are listed in cents to one decimal place. >80% of the time the last digit is a nine, the rest of the time it’s most commonly a 5. I’ve seen other odd digits rarely, with even numbers just about unheard of. But what you actually pay will be rounded to the cent, or to the nearest 5¢ if you pay in cash.
