Is it normal to be able to shut your nose from within?

Just for perspective: I am a man in my mid-40s and for as long as i can remember i had this question... is it normal that i can shut my nose close just with some muscles?

I always wondered why some people hold their nose shut with their fingers while jumping into a pool or when exposed to some horrible smell... i never had this need. Changing my sons diapers? No problem! Cleaning the latrines while in the army? Just a breeze!

Ehm... yeah... just thought about this...