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:
9. Luke Molyneux 7
Forged a good opening midway through the first half but flashed a wicked shot wide of goal. Did similar at 2-0 from a pinpoint Senior centre. Linked well with Lee as Northampton were gradually worn down. Photo: Howard Roe/AHPIX LTD
10. Elliot Lee 8
Again led the line, albeit as an auxiliary centre-forward. Saw a shot diverted onto a post first half but buzzed about nicely and got his reward with a poacher's finish for the opener just after half-time. Serenaded by the away end, throughout. Photo: Connor McMain/AHPIX LTD
11. Hakeeb Adelakun 8
Frustrating show first half, with nice entries into dangerous areas only to then botch his shot/cross. Improved plenty after the break with a touch of magic as he fired home a lovely strike to double the advantage and was a constant menace. Photo: Connor McMain/AHPIX LTD
12. George Broadbent 7
Replacement for Clifton with 15 to go. Not much involvement - until his superb strike to put the gloss on the win. Photo: Andrew Roe/AHPIX LTD