Issue with viewport rotation values.

Alright, this has been bugging the life out of me since I started using unity a year and a half ago.

Why is it that when I hold down ctrl to snap rotate an object it also goes to values with long decimal numbers (i.e. 45.0000003 or 89.9999997) instead of just 45 or 90? It goes to 45 or 90 sometimes.

Also it seems that duplicating(ctrl d) some objects will sometimes change its rotation values like said values above.

All these slight changes make noticeable gaps in my grid based game.

Forgive me if this such issue has been answered already, I haven't the slightest clue on how to search for such a topic without getting irrelevant stuff.

Thanks, I hope to understand why this is so.