Infinitely many. It depends on the accuracy to which the numbers were given prior to rounding.
It is 600000.
600000
0
There are infinitely many such numbers.
Ten of them.
It is 600000.
600000
It is 600000.
It is 600000.
It is 600000.
It is 600000.
It is 600000.
It is 600000.
It is 600000.
600000
It is 600000.
It is 600000, as in the question!