First, find the rounding number, it is either in the tens place, ones, tenths, hundredths, so on. Then, take a look to the number after (on the right) the rounding number. If the number after the rounding number is round-down number (0, 1, 2, 3, or 4), then the rounding number will keep its value and will not change. If the number is round-up (5, 6, 7, 8, or 9), then we will add one value to the rounding number.
Example: Round off 356 to the nearest tens.
Our rounding number here is 5, because it is what on the tens place. The number after it is 6(round-up number). So we will add one value to the rounding number (5), and it will become 6. Lets replace all the number on the right of the rounded number to zero (0).
So, 356 round off to the nearest ten is 360.