7. Gas has been priced to a tenth of a cent since the 1930s
That coincides with the federal government instituting a $0.001/gal tax. Also, because gas was generally between 20 and 30 cents at the time, fractions of a cent made a much more significant difference than they do today.
8. Your final total, though, is rounded
It’s pretty basic: If your total ends in 0.4 cents or less, it’s rounded down. 0.5 or up goes up.
9. The federal gas tax hasn’t changed since 1997
It was 18.4 cents in 1997, just as it is today. The fluctuation you see is actually the state taxes, which on average run just over 30 cents per gallon.