At one point dimes were made of more valuable silver, while nickels and pennies were copper alloys, but today all US coins have the value they have because people accept them as such; they are fiat currency just like paper money.
Whereas a penny, even though they switched to cheaper metal, is roughly worth a cent – if a dime was still made of silver it would be worth roughly $3, or if made a silver and worth $0.10 it would be not much bigger than a pencil point.
Current dimes made for circulation have about as much silver as seawater. However, the mint does sell special dimes that contain the same amount of silver that a dime used to have.
A nickel on the other hand has metal content approximately worth its value. That is why the government is looking into ways of making them for less.
There is a children’s book out there about a little boy whose father gives him a dollar. His friend offers to give him two quarters for the dollar, and he is so excited that now he has TWO pieces of money. In the same manner, he exchanges the two quarters for three dimes, then for four nickels, and finally for five pennies.