Question 598416
Because any real number can be rounded to the nearest tenth (e.g. there are no two "nearest tenths" -- even if we have a number such as 3.45 we normally round up).


In other words, each number is mapped to exactly one output (or y-value). If you are curious, here is a graph:


http://www.wolframalpha.com/input/?i=f%28x%29+%3D+round%28x%2C.1%29