" why do you think we round up when a 5 is the next digit to the right of the place in witch we are rounding ? "
i'm guessing it has something to do with numbers starting out at zero ?
Do you think it would be reasonable to give everytime all the numbers in pi for example?
One other thing... when you take a reading, you always take it to the nearest reading you can measure. If the exact length of something was 1.0652 cm, you will only be able to measure a length of 1 cm with a common ruler.
Rounding off is a means to simplify numbers and remove unnecessary details. This eases work. Where some accuracy is required, then you don't round off.