To round to nearest hundred, look at the tens digit: if it is 5 or more round up otherwise round down; 2 is not 5 or more, so round down:
5921 → 5900 to the nearest hundred.
It is 300 when rounded to the nearest hundred
916 rounded to the nearest hundred is 900
It is already rounded to the nearest hundred thousandths. Rounded to the nearest thousands would be 87.381.
0
0
0
678 is rounded nearest hundred is 700
300
409381900
8900
0
10900