Karl bought 5 copies of a certain videotape that was on sale at 20 percent less than the regular price. He had 4 of the tapes wrapped at a charge of $0.50 per tape. There was a 4 percent sales tax on the reduced price of each tape, but no sales tax on the wrapping charge. If Karl paid a total of $168.40 for the 5 tapes, including the wrapping charges, what was the regular price, excluding sales tax, of one copy?