Cent refers to the hundredths place, therefore because gasoline costs $2.379 per gallon, you refer to the digit (number) in the thousandths place to determine whether you round up or down. Because the digit, 9, is equal to or above the number 5, you would round the digit in the hundredths place up. Therefore the 7 becomes 8, and you get rid of the 9.
The answer is $2.38 per gallon.