Spiritually Speaking, Very large factorial numbers always end with a string of what repeated digit?

IJR takes part in the TUESDAY TRIVIA contest from Ken Jennings every Tuesday, hence the name TUESDAY TRIVIA. Most of the time IJR can answer all seven questions, but this one has IJR stumped. Can you help? IJR knows this is the wrong category, but you people are the bet on Y!A, and if one of you don;t know the answer, no one will.