How do you round to nearest square mile?

When rounding to a specific place, take a look at the digit immediately to the right of the target, in this case, the tenths place. If that digit is 4 or less, zero everything to the right of the target out. If that digit is 5 through 9, increase the target by one and zero everything to the right of it out. If the target is a 9, increasing it will turn it to zero and increase the digit to the left of the target by one.