For residential, 15A Duplex receptacles on a 20A circuit are fine according to NEC. Basically, as long as you have more than a single 15A receptacle on a 20A circuit (a duplex counts as two) you're fine.
That said, you may have local amendments or an entirely different electrical code adopted by your AHJ.
It's also something you don't want to argue with a misinformed inspector about because he can make your life hell. You have to pick your battles and this ain't one of them.