Not taking credit cards will cost you business in a retail location.
What is defined (in this thread) as "most cash businesses" would be to me businesses that would typically allow someone to pay with a credit card.
That wouldn't be a local bodega allowing some to pay for a pack of gum with a credit card. It would be a business allowing cc use in a typical case where the per transaction charge is not significant and you don't stand to loose business because you don't accept credit cards.
Examples:
You run a restaurant and your average ticket is $45. If you don't accept cc's you will generally loose business.
You run an ice cream stand and your average ticket is $5. Less expectation of being able to (or needing) to use a cc for a small transaction like that. Chance of loosing business: significantly less.
Say you charge the customer $5: 2% + $0.30 is $0.40--8% of the total.