Unless stores pass the tax on to consumers directly, it's not going to cause the delared desired affect. However, given that it's supposed to only affect stores that have over $2 million in grocery sales, it's essentially a supermarket tax instead of a grocery tax. So in the name of "helping the environment" this tax would give more expensive convienence stores and neighborhood grocerys an advantage. Gotta love the law of intended consequences.
Everything is already expensive in San Francisco. This doesn't change a damn thing.