Do 20 nickels equal 1 lb?

No. US nickels weigh 5 gm each so 20 of them weigh 100 gm, or a bit more than 1/5 of a US pound (453.6 gm).

You can easily determine this by comparing the weight of coins from your pocket change with a loaf of bread, soup can, hot dog package, or other item that weighs 1 pound.