Managerless County had the better of the game in the battle of the high-fliers and should have claimed all three points against the Millers, who had Nick Fenton sent off.
Matt Richie forced a fine save out of Rotherham keeper Andy Warrington and Mike Edwards skied the rebound over from six yards.
Neal Bishop and Lee Hughes both headed wide as the visitors domination continued, before they wasted their best chance of the half.
Ben Davies whipped in a fine cross and Edwards sent his header crashing into the bar with the goal gaping.
Rotherham improved after the break and Kasper Schmeichel was called into action for the first time to deny a Kevin Ellison effort.
Eventually County's numerical advantage told and they finished the game strongly. Luke Rodgers had a low drive well saved by Warrington before Pablo Mills produced a fine block to deny another Rodgers effort.