What tweening you are using? try linear, or others, and see if it makes a difference
also, are you sure your target is 0 exactly. maybe the transform rotation is the source fo the problem, not the action itself.
I do use belt and braces sometimes ( when I don't want to know what the problem is...) so I do sometimes force the end result, and do not rely on itween or the technic I used to get there, I just force it to make sure it's perfect. It should tho, but you know...