Round this number to the nearest 1000th place.
I was taught that the conventional way, when the last integer is an exact 5, is to round even down and round odd up.
Examples: 100.1245 the four is even so this rounds down to 100.124
100.1235 the three is odd so this rounds up to 100.124
The premise is that there there are an equal number of odd digits as even digits, so the rounding balances out, over the long run. I see that my method conflicts with CPhill. You might check with your teacher and see how s/he wants you to do it.