Every modern nickel weighs 5.000 grams or 0.176 ounces. The modern nickels are known as Jefferson nickels and they have been minted since 1938. Their composition is 75% copper and 25% nickel. From 1942 to 1945 the government issued the silver 35% silver Jefferson War Nickels however these coins still weigh exactly 5 grams.
Before the Jefferson nickels there were other series such as the Washington nickel, Shield nickel, Buffalo nickel and the Liberty Head V nickel. Each of these series also weigh 5 grams.
The earliest nickels weighed much less than 5 grams. The first nickel ever produced was the "half disme". It was produced in 1792 and it weighs just 1.2 grams. Next came the Flowing Hair half dime (nickel) that weighs 1.34 grams. The Draped Bust and Capped Bust half dime series followed and they each weigh 1.35 grams. Starting in 1837 until the Coinage Act of 1873, the nickel went through changes so the weight wasn't consistent. In 1837 the Seated Liberty half dime was minted with a weight of 1.34 grams. In 1853 this coin's weight changed to 1.24 grams. It continued to be minted with a weight of 1.24 grams until the series ended in 1873.
All the nickels found in your change will be 5 grams. Because each modern nickel is exactly 5 grams, many people use nickels to calibrate their scales. You can place a nickel on your scale and then take note of the weight. You can then adjust the scale up or down by the difference in weight.