The discount for cash thing was based around credit card terms of service

Most credit cards used to require merchants to agree to charge the regular price for credit card transactions. If they found out a merchant was charging customers 2-5% more for credit cards to cover fees, they'd cut off the merchant so they could no longer accept their card. VISA would do it a lot, and no longer being able to accept VISA is a huge blow to any business

Businesses would use the workaround of a cash discount to avoid angering the credit card companies, but more recently it isn't necessary. I'm not sure if it was a regulatory change or market pressures, but I haven't heard of a merchant getting dropped for that in a while