Do Part Rolls Count?

I’m new to baking and did my first endorsements yesterday, I have a couple of questions regarding rolls if anyone can help me out?

Do only full rolls count towards rights? for example if I one 2.5 rolls, is that half roll been considered or is it wasted?

As per the above if part rolls don’t count, what happens if someone delegates me half a roll? clearly they will expect their fees for their contribution but from my point of view it wont be counting towards rights hence I wont be getting extra rewards from it?