How much is a roll of 1938 nickels bu worth?

What you saw as an "E" is not a mint mark, and is actually an "F", the monogram of the coin's designer James Fraser.

The mint mark on buffalo nickels is under the Words FIVE CENTS.

Plain (no mint mark) and "S" 1936 nickels are worth a dollar or two in average condition. "D" coins are worth slightly more.