How many nickels fit in 1 gallon milk jug?

If the jug was in the form of a cylinder with a diameter of 0.835 inches and a height of 421.8 inches (=35.2 feet), then it would hold 5478 nickels. For a jug of ANY other shape it would hold fewer. This is due to gaps between the coins and the sides of the jug as well as between coins. The extent of this difference would depend on the exact measurements of the jug.

Incidentally, most ordinary rooms are less than 12 feet high so this jug would need a three storey house!