I often don't carry cash or coins anymore (like many of us).  One grocery store I frequent wants you to deposit a US quarter to use a shopping cart.  I tried other 3d models and they didn't seem to work well or fell out of the cart.  I decided to try my hand at making what seemed like a simple model.

The uploaded file is version 2, which has a larger key ring hole and a ridge around the keyring hole to lessen wear from rubbing on a key ring.