It does to me, reaching orgasm or ejaculating causes you to release a hormone, that makes you feel tired
It definitely doesn't have that affect on me.
I'm already tired, but have sexual tension, then relieving that sexual tension will definitely make it easier to fall asleep.
But if I'm not tired, having an orgasm to relieve sexual tension will not make me tired. On the contrary, I often find it has just the opposite affect and makes me feel revitalized.
I think the reason most men want to roll over and go to sleep after having an orgasm is simply because they usually have sex at night and they're naturally tired anyway. Moreover, if they put out a lot of work and effort building up to the act of having an orgasm (which may have included additional effort to induce an orgasm in their partner), they may want to roll over and go to sleep after that just because it was a lot of work.

But seriously, having an orgasm in and of itself, doesn't automatically make me tired. It can actually serve to make me feel more alert and clear-minded than I was before I relieved that sexual tension.
All people are not the same though, I'm sure.