Processing credit cards online requires two pieces: the payment gateway and the merchant account. These are both separate from the shopping cart. The merchant account is basically the ability to accept various credit cards and the gateway is the online version of the credit card swipe machine you see at a retail store.
Get your bill from the same company as your cart. For only $10.00/month and $0.10 a transaction billed on your monthly Veracart account will only simplify your life.