Daniel Nardiello's slotted penalty gave the Millers the lead after Mark Bradley was tripped by Ben Harding in the area just before half time.
Liam Ridehalgh went close for Rotherham in the second half before Ben Pringle doubled their tally with a curling effort from the edge of the box with his left foot.
David Noble got the third three minutes later with a well timed run into the box and a fine sweeping finish on his first start since October, before Clarke Carlisle's injury-time header reduced the arrears.
Source BBC Sport.