Practice rounding numbers off to the nearest 10. This means rounding them either up or down to the nearest value divisible by 10. For example, 23 would be rounded down to 20, and 345 would be rounded up to 350. Notice that any value of 5 or above is rounded up and below 5 is rounded down.
Do some rounding to the nearest 100. Use the same principles you used when rounding to the nearest 10. The number 568 is rounded up to 600, and 423 is rounded down to 400.
Use the same principles of rounding to round to the nearest 1,000. For example, 1,398 is rounded down to 1,000, while 1,947 is rounded up to 2,000.
Round numbers before adding or subtracting to learn estimation. What you round to -- 10, 100, or 1,000 -- will depend on how accurate the number needs to be. For example, rounding 678 + 129 to the nearest 10 would make the problem 680 + 130. The estimated answer is 810, while the actual answer is 807. If you were to round to the nearest 100, the estimated answer would be 800.