Maybe even put 5 in an extra magazine in another pocket.
So if you are actually carrying the other rounds in another magazine you are not really reducing any weight. You are just limiting yourself on the rounds you can fire before you have to reload.
I am assuming you carry a gun for self defense and the worse case scenario right? Well wouldn't it be better to carry a full magazine to be better prepared for the worse case scenario? Ghost1958 brings up some good points. I see the thought process you have and see how this question came up but I think it would be simpler and better just to carry as many rounds in a gun as it can hold.