Employer docks pay and blames it on their clock in system

I am usually scheduled 8-5 and our punch in/out system has an exact time on it, so I know for a fact that I clocked in at 7:58 and out at 4:59.57. My manager then informed me that our clocking system works in 15 minutes increments and that I would actually be paid for 8-4:45. Is this legal? Seems like wage theft to me