Charges for using credit cards?

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I allways have $100 to $300 in my wallet or stashed away at home. I may only go to the bank once a month but when I'm there I cash a check so I always have cash. My friend who owns a tackle shop said if someone spends under $10 in their store and uses a charge card they don't really make any money off the transaction. That's been years back sense he told me that and I'm not sure how much that has changed over the years.