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:
1. Thimothee Lo-Tutala 6
Hardly tested all afternoon with the Cobblers proving powderpuff in attack. Cautioned for time-wasting and couldn't prevent the hosts nabbing a consolation right at the death. Photo: Connor McMain/AHPIX LTD
2. Jamie Sterry 7
Competent performance although in truth the entire defence was under-worked. Saw an ambitious long-ranger parried away by Burge second half and then forced an even better stop with a late free-kick. Photo: Connor McMain/AHPIX LTD
3. Matty Pearson 8
Nice ding-dong all afternoon with Eaves, who kept him honest. Plenty of clearances and some well-timed blocks, too. Photo: Connor McMain/AHPIX LTD
4. Sean Grehan 8
A few loose passes but defensively was spot-on. Produced a javelin-esque throw that led to Lee's opener. Photo: Howard Roe/AHPIX LTD