For the USA, an unworn 5 cent nickel weighs 5 grams. When I was testing one of those tiny portable scales that are battery operated, I would use 1, 2, and 3 nickels to determine if it was close to being accurate.
Indeed. Calibrating scales with nickels is a well-known trick in certain circles, including, but not limited to, organic chemistry labs. It won't do for analytic weighing, but for sanity-checking a scale before weighing out reagents, it does the trick.