This is a bit confusing to explain. Sorry in advance for the sloppy explanation.
First step is to find the number in the tens place.
7,997
The bolded nine is in the tens place. Now we need to find out whether to round up or down. For that we look to the number to the right of the tens place.
If the number is less than 5, we round down.
If the number in five or greater, we round up.
In 7,997 the number to the right of the tens place is a 7, so we round up.
But since 9 is already as high as you can go in the tens place, we add 1 digit to the hundreds place and change the tens place to a 0.
Aaannnddd since that number is a nine as well we add 1 digit to the thousands place and change the hundreds place to a 0.
So 7997 becomes 8000.
