An injury-time strike from midfielder John Mullin was the icing on the cake for the Millers as they continued their march away from the drop zone.
Ronnie Moore's mean machine secured a fourth clean sheet in five games as strugglers Bradford extended their goal famine to four matches.
Mullin's 25-yard free-kick flattered the visitors, who rarely threatened despite going ahead through a dubious penalty, but City were left cursing their luck again at both ends of the pitch.
The in form Millers, who are now unbeaten in seven matches, started slowly and their opener after 14 minutes was against the run of play.
City made the early running only for another defensive lapse to cost them dear.
Rotherham striker Martin Butler darted into the box as the Bantams hesitated and when Jason Gavin sent him tumbling referee Paul Robinson awarded the penalty.
Jamaican international Darren Byfield coolly sent keeper Mark Paston the wrong way to register his eighth goal of the season and although City responded with some neat approach play they could not find the vital finish.
Michael Branch, Gareth Farrelly and Andy Gray all went close to levelling but when referee Robinson waved away a Bradford penalty appeal it never looked like being their day.
At the start of the second half a teasing cross from Tom Kearney was just too strong for Branch, but with Millers skipper Chris Swailes and Guy Branston in good form the breakthrough looked unlikely.
Paston raced from his box to make a crucial tackle on Byfield and City full-back Paul Heckingbottom saw his free-kick go inches over the bar.
With the seconds running out Butler was sent flying again and Mullin took advantage to beat Paston with a well-struck drive.