Rounding and Precision

Rounding trims a number to the precision you actually need. To round 3.14159 to two decimals, look at the third decimal: it is 1, less than 5, so you round down to 3.14.

The catch is that small rounding errors add up. Round at every step of a long calculation and the final answer can drift far off. That is why banks keep extra hidden decimals and serious computation holds onto many digits — the goal is to stop tiny errors from piling up across millions of operations.