The Millers were 2-0 up inside 19 minutes thanks to goals from Ryan Taylor and Marcus Marshall, but they were quickly pegged back by Abdul Osman and Andy Holt who rescued a point for the Cobblers.
Sampson said: "I was delighted to get back into the game. The first half was quite open, end to end stuff, and Rotherham scored two really good goals - two quality goals. And there were two really good goals from us.
"I would not like to say what I was thinking when their second goal went in, but I am just happy with the way the team responded.
"We maybe had the better of the first half and the second half was pretty even. We had one real clear-cut chance but we just failed to put it in the net.
"In adversity, which we have been through quite a bit this season, they keep responding. We still have a long way to go because we are near the bottom of the league but I have never doubted or questioned their character."
Source: PA
Source: PA