Because it ends in a 3 and gets rounded down. 63 is nearer to 60 than it is to 70.
60
It is 60
60
60 to the nearest ten is 60.
63 rounds to 60.
60
60
55 rounded to nearest ten is 60
60
If you are rounding to the nearest tens, it is correct that 63 is rounded to 60.
60
60