Don’t worry; your credit card cash-back rewards from regular purchases are not taxable. They are considered rebates in the tax code, except when earned for purchases of cash equivalents like money orders or debit card reloads.
Thomas M. Spade, a Senior Instructor of Accounting at the College of Charleston explains, "Redeeming rewards against a credit card balance isn’t taxable; it is generally treated as a rebate. And a rebate is generally treated as non-taxable for individual taxpayers in accordance with Revenue Rulings 76–96."