When you round a number, the digit in the number that helps you decided to round up or down, is one digit to the right of the digit, you picked to round.
Rule -
Pick a digit to round up in the number. Move one space to the right of the digit you picked. Then, if the digit to the right is at least 5, meaning that if it’s above or equal to 5, then round the digit you picked up by 1. However if the digit to the right is lower than 5, then the digit you picked stays the same. Remember that anytime you round, either down or up, anything to the right of the digit, you picked becomes 0.
For example, let’s use the number, 1087, and we picked the digit 8. We have to look at the digit to the right, of the digit we picked, which is 7, to see if we need to round up or down. Since the number is above 5, then we have to round 8 up. Anything to the right of the 8 become 0.
Hope this helped!