What can I do with 'very rare' coins?

I've found a bunch of golden coins in Coin Crypt which are describe with the phrase "Very rare". They're also listed with a value of $75 (whatever that means).

They don't appear to do anything useful in combat either. They have the same description and when I used one on an enemy I didn't notice any effect.

What are these coins for? Are they just there to boost your total $ value?

Based on my playing so far, it seems that these rare coins are used in shops, or for donating to the Loot Gods.

The more rare the coin, the higher the monetary value, and thus the more money you will have to spend at the shop or donate to the Loot Gods (unless you are playing as the Demon, who's money is counted using negative currency).