Why Do Gas Prices End in 9/10 of a Cent?

Gasoline is sold at x dollars, x cents, and then an extra 9/10 of a cent. This makes no sense, except when it does. Simon Whistler of Today I Found Out looks into the history of fractional gas pricing and why it has stuck around so long. In the middle, he has to digress to express amazement at US gas prices, from the perspective of someone who doesn't live in an oil-producing country.