The closest hundred to 29 is zero. You can think of it in terms of money. If you have 29 cents and you want to know approximately how many dollars you have, the answer is none.
100
30
593 656 rounded off to the nearest hundred is 593 700.
409 to the nearest hundred is 400
10100
409,381,900
900
2,600
To the nearest hundred, 165400
It is 7300
3600
To the nearest hundred, 3623400