gas prices -- what's the deal with the .009?

[Bill McBlueState]

This came up in another thread -- does anyone know why gas prices are always posted to three places after the decimal?

$3.299, for example.

I understand that it makes the gas look ever-so-slightly cheaper than it really is, since people tend to ignore the nine-tenths of a cent. But you don't see Twinkies or anything else sold for fractional cents.