$$\text{Rounding off is a type of estimation. Rounding off means a number is made simpler by keeping its value intact}$$ $$\text{but closer to the next number.}$$ It is done for whole numbers, and for decimals at various places of hundreds, tens, tenths, etc. Rounding off numbers is done to preserve the significant figures. The number of significant figures in a result is simply the number of figures that are known with some degree of reliability.