It is my understanding that companies are forbidden from offering differential pricing for cards and cash. At the very least, prices on the shelf must include credit card processing fees in the base price. Sometimes small-time businesses will offer cash discounts, but most retail and grocery places won't.
Every gas station I've been to this year (not that many, my car is electric, so only when I'm filling my wife's car) has had a lower price for cash than credit, and this price is often on their big sign in front of the entrance. This is in California, if it makes a difference.
VISA and MasterCard rules prohibit this, unless specifically allowed by local law.