With the game seemingly heading to the break with the scores level, Chris Ramsey's men went in front through Dutch striker Chery, who slotted home Charlie Austin's lay-off to bag his first goal for the club.
Matty Phillips almost gave QPR a first-minute lead but the winger's header glanced marginally wide.
Rotherham responded well and Matt Derbyshire could have put the away side ahead, but shot straight at Robert Green.
If there was any doubt about his first chance, Derbyshire definitely should have given the Millers the lead on the half-hour mark, but the former England U21 international somehow fired wide from close range.
Just as Rotherham will have been expecting to have done enough to go in at the break level, Chery turned the game on its head with a crucial strike.