When rounding to the nearest 100 you need to look at the 10's place. Anything 5 and above rounds up and below five rounds down. Since the tens place in 990 is a 9, the nearest 100 is 1000.
to the nearest hundred 990 would be 1000 because 90 is above 50 and even if it was 950 you would still round it to 1000 because 50 AND above rounds up and 49 BELOW rounds down.
