There are other considerations that need to be fixed first. Fraud protection has historically been stronger for credit cards than other means of payment in the US. Likewise cash back vs not.
So the cash back is just a partial refund on your credit card processing fees.
Cash also has cost - employee theft, risk of getting robbed while taking it to the bank, it takes more time to handle, etc.
If I had a business, I would not accept cash at all.