Oh, dude, rounding 109 to the nearest 100 is like, super easy. You just look at the tens place, which is zero, and since it's less than 5, you don't need to do anything. So, 109 rounded to the nearest 100 is still 100. Easy peasy, lemon squeezy.
To round 109 to the nearest 100, you look at the digit in the tens place, which is 0 in this case. Since 0 is less than 5, you keep the hundreds place digit the same, which is 1, and change all digits to the right to 0. Therefore, rounding 109 to the nearest 100 gives you 100.