The win - thanks to second half strikes from Elliot Lee, Hakeeb Adelakun and sub George Broadbent - stubbed out any vague fears of the drop as Grant McCann's men confirmed their place in League One for next season.
The first half was a fairly sleepy affair, perhaps understandable given the hosts' relegation was confirmed in midweek. Rovers had the better chances to open the scoring with first a Lee snapshot deflecting wide before Luke Molyneux saw a shot just clear the right-hand post after a zippy pass was fired into him by Harry Clifton.
The visitors came even closer when Lee diverted a shot towards goal that was deflected onto a post before being hacked away by the scrambling Northampton defence.
Rovers picked up where they left off after the restart and after Adelakun's effort went wide of goal, the breakthrough finally came. Sean Grehan launched a huge throw-in that was nodded on and ended with Lee firing home from a couple of yards out.
That lead was duly doubled shortly afterwards when Adelakun beat goalkeeper Lee Burge after bending a shot in via the right-hand post as he advanced towards goal. The icing on the cake was added late on when substitute Broadbent produced a terrific, curled effort that flew past Burge.
The only downside was Rovers couldn't keep a clean sheet as Cameron McGeehan prodded in from a yard out right at the death.
Here's how we rated the Rovers players at Sixfields:
5. Jack Senior 7
Kept Fornah quiet in the most part. A target for Northampton boo boys after a heated incident just before half-time. Some good interventions as a full-blooded showing, as is to be expected now. Photo: Howard Roe/AHPIX LTD
6. Robbie Gotts 8
Lovely jinks and touches and seemed to be everywhere. Another industrial and gritty engine room showing from him. Photo: Connor McMain/AHPIX LTD
7. Owen Bailey 7
Skipper sent a header over the bar first half. Tenacious showing and got an assist for Adelakun's goal. Always in the box ready to pounce on any loose balls. Photo: Howard Roe/AHPIX LTD
8. Harry Clifton 7
Glanced a header wide of goal in the first half. Kept at his task and came close on another few occasions as well as chipping in with key passes. Photo: Howard Roe/AHPIX LTD