Rounding off Decimals

I know how to round off very decently but I have to ask this question.

I need to round off 242.48407 to the nearest thousandths.

I look at the number to the right of 4 and notice there is a zero there.

Would the answer be 242.484 or 242.485?

Thanks

Look at the digit after the thousandth one. If it is larger than or equal to 5, we round up. Otherwise, we round down.

So: