When you round numbers to the nearest 10, 100 or 1000, you must consider whether your number is closer to e.g. 30 or 40, 300 or 400, 3000 or 4000.
For example, If you are asked to round 3457 to the nearest 100.
If you counted up, the first number in the 100 times table would be 3500
If you counted down, the first number in the 100 times table would be 3400
3457 is between 3400 and 3500
But it is closer to 3400
Examples
359 is closer to 400 than 300.
359 is 400 when rounded to the nearest 100.
75 is halfway between 70 and 80. In this case, we round up to 80.
3499 is nearer to 3000 than to 4000.
3499 is 3000 rounded to the nearest 1000.