The round function enables you to truncate values to the number of decimal places you desire. This could be in fractions of a whole value e.g. hundredths and thousandths of whole number, or as large numbers, e.g. rounding to the closest million or billion.
There are some very similar functions, ROUNDUP, ROUNDDOWN and MROUND. In addition there are some complimentary functions such as FLOOR and CEILING.
These functions all perform the same way with specific variations. Round follows the 4/5 round principle. That is if the number ends in 4 or lower it rounds down, and if it ends in 5 or higher it rounds up.