Remember that
To Round a number
a) Decide which is the last digit to keep
b) Leave it the same if the next digit is less than 5 (this is called rounding down)
c) But increase it by 1 if the next digit is 5 or more (this is called rounding up)
In this problem we have
81,485
1,485 < 1,500
that means
81,485 ---------> 81,000