you look at the last two digits. If they are 49 or less, you just replace them with zeros. If they are 50 through 99, you still replace them with zeros, but you also add one to the 3rd from the last digit. If the last two digits are 00, you just leave the whole thing alone - it is already rounded.
so,
273,568 is rounded to 273,600
449 is rounded to 400
1251 is rounded to1300
49 is rounded to 0
451 is rounded to 500
51 is rounded to 100
253 is rounded to 300
400 is rounded to 400
372 rounded to the nearest hundred is 400
96 round to the nearest ten=100
400
100
10,000
200
100
It is 71,400 rounded to the nearest 100
12398872348387264762873648632800 Confuse?
100
100
4400