Lots of businesses in general like to add charges when paying with a card. The *type* of card matters. The difference being credit or debit.
Check your states laws regarding adding a fee for those paying with *credit* cards. Also check the rules for the card network- Visa, MC, AE, etc. They may have caps on charges or not allow surcharges.
Debit card fees are generally *illegal* thanks to the Durbin Amendment. Look it up.
Discounts are favored over surcharges. For example- My menu says $7. It also says "credit card purchases are menu price + tax + Square fee of 2.6% + 15 cents".
I.e. Cash price is $7 *including* tax therefore a cash discount because the tax (in my county and state) on $6.56 is $0.44 for a total of $7.
Double check with you POS provider, card network, state, county, and local laws for what you are required to add and what you cannot add.