What is on the tails side of a US nickel?

From 1938 to 2003 and 2006 to the present, it is Thomas Jefferson's home, Monticello.

The two reverses of 2004 honoring the Lewis and Clark Expedition depict the Indian Peace Medal which they presented to Native American leaders they dealt with on the trip and the keelboat they used to travel up the Missouri River. The series continued in 2005 with a bison (American buffalo) and a scene depicting their first view of the Pacific Ocean.

Before that:

> Shield nickels (1866-1883) - the number 5

> Liberty nickels (1883-1912) - the Roman numeral V, for 5.

> Buffalo nickels (1913-1938) - guess what, a buffalo!