I would not experiment with that, especially with modern coins that are mostly made from cheaper metal alloys.
I wouldn't worry about the melting point much, but it's just not very practical. It's too small, and using fiat coins to store real money doesn't feel right

This reminds me of collectibles: some people still hold 50 BTC inside a tiny piece of paper inside a collectible coin. There's no backup, and it's as fragile as it gets.