Unless there are rare coins in the collection, it is probably only worth the face value of the coins. Currency does not have to be declared unless it totals
$10,000 or more (
FinCEN Form 105).
Here is a pictorial guide:
If there are rare coins, you'd probably have to declare their total value if it exceeds $800.
ETA: Proof and Mint sets are also worth more than face value:
Modern U.S. Proof Set Values and Prices