When rounding a number to the nearest hundred, you look at the digit in the tens place. In this case, 4500 has 5 in the hundreds place and 0 in the tens place. Since 0 is less than 5, you would round down to 4500.
Oh, dude, rounding numbers is like, so easy. 4500 rounded to the nearest hundred is 4500 because it's already at the nearest hundred. It's not like we need to change anything here, so no need to stress about it.
Well, honey, 4500 rounded to the nearest hundred is simply 4500. Ain't no need to change a thing when you're already sittin' pretty on a nice, round number. So, there you have it - 4500, no muss, no fuss.