There are 40 nickels in $2. Nickels are valued at 5 cents, and $2 is 200 cents. Therefore, 40 nickels and $2 have the same value.
Nickels are considered small change and are frequently dispensed at points of sale as change for a cash purchase. If you specifically wish to purchase nickels, any bank can sell you a $2 roll containing 40 nickels. If you wish to deposit nickels into your bank, ask the bank for a nickel sleeve, stack 40 nickels and roll them into the sleeve. You can then deposit the rolls of nickels in your bank account. A $2 roll of 40 nickels can be heavy; two paper dollars have the same value and are much more portable.