Ignore the digit in the ones position.
If the digit in the tens position is 5 or greater, then raise the digit in the hundreds position. If not, then leave the digit in the hundreds position the same.
Drop all digits that aren't in the hundreds position by making them 0's.
The answer is: 500
100 rounded to the nearest 529 is 0.
500
129
500
500
round 90 to the nearest ten
372 rounded to the nearest hundred is 400
300
2,222 rounded to the nearest 100 is 2,200.
100
100
100
10100
4198 to the nearest 100 = 4200
100