When you round off a number, you look at the digit just to the right of the one you want to round off to.
For example, if you want to round off to the underlined digit in 89,100 then you look at the digit to the right: the 1. It this digit is 5 or more, then you change this digit and all the other digits to the right into zeros and you add one to the digit that is underlined. If it isn't 5 or more, then you still change it and all the digits to the right into zeros, but you don't add one to the underlined digit.
In this case, 1 is certainly less than 5, so we turn it into a zero and we turn all the digits to the right into zeros (well, they are already!). So the answer is 89,000.
Let's take a look at another example: how do you round off to the underlined digit here: 76,912? Look at the digit to the right of the underlined one. It is 9, which is certainly 5 or more, so we still change it to zero and change the 1 and 2 to zeros as well. But this time we add one to the underlined digit. So our answer is 77,000.
Hope this helps!