Andy Holt had given the Cobblers the lead just after the break before Waide Fairhurst's third goal in three games levelled matters for the home side.
It was the Cobblers' fifth straight draw, but Sampson felt they should have come away with all three points, saying: "It's getting to be a bit of a grind now with five on the spin."
He added: "We are disappointed because we thought we could have won the game.
"We hit a post and we thought there should have been a penalty for a foul on Billy McKay.
"I'm not too pleased with the referee because I thought there was a foul too on Michael Jacobs in the build-up to the Hereford goal."
Source: PA
Source: PA