Matt Ritchie's brilliant long-range strike seven minutes before half-time gave Di Canio's men the lead before second-half goals from Benson, Aden Flint and substitute Alan Connell sealed an emphatic win.
Ritchie sparked a dull encounter into life by picking up the ball on the right touchline, cutting in onto his left foot and lashing an unstoppable shot past Martin into the top corner.
Benson doubled Swindon's lead on 51 minutes. Captain Paul Caddis' threaded through ball was dummied by Simon Ferry and Benson calmly lifted his shot over the advancing Martin and into the net.
Benson claimed his second in the 65th minute by arriving at the near post to slot home Lee Holmes' cross and just two minutes later it was 4-0 as centre back Flint nodded in Ritchie's corner.
Connell crowned a fine team performance five minutes from time by turning in Luke Rooney's attempted shot from close range.