Is it considered leaving the scene of an accident if when parking you bump the car in front of you causing no damage and leave and go in a store?

The adjective "bump" is so subjective as to have no meaning.

Was it a minor bumper "tap" or a full-fledged "whack" that rocked both vehicles?

What you consider "no damage" may not be what the owner of the other vehicle thinks.

Unless it OBVIOUSLY falls into the category of a bumper-kiss, you should try to locate the other owner or, leave your contact information under the other vehicles wiper.