With practically the last kick of the game Madjo was on hand to roll the ball into an empty net after Blues stopper Ashley Bayes could only parry Michael Brough's drive into his path.
Though other results went against Rovers, who crashed to the bottom of the table because of Scarborough's win over Burton, the point was just reward for a side that may have lacked the finesse of their high-flying hosts but more than made up for it in desire.
Rovers started brightly with Brough and Mark Beesley both forcing Bayes into saves after low drives from the edge of the box.
But Grays looked sharp going forward too and Dennis Oli should have done better when he was released by Aaron McLean but lacked any real conviction with his finish.
The ex-QPR man made amends for that miss shortly after when he was left in acres of space to head home Glenn Poole's wicked free-kick to give the hosts the lead.
The visitors though were on level terms shortly before half-time when they won a controversial penalty.
John Nutter was harshly adjudged to have hauled down Alex Meechan, who went down in theatrical fashion and Brough rolled home the penalty.
Julian Alsop missed a trio of headers at the start of the second period before Grays regained the advantage.
McLean's pass caught Sekani Simpson sleeping and Glenn Poole slid the ball beneath Ryan Clarke.
Poole then hit the bar with a rasping 30-yard volley and Meechin blazed over for Rovers before Madjo came to the rescue and struck the equaliser deep into injury time.