Round a number to the desired number of decimal places — see standard rounding, rounded down (floor) and rounded up (ceiling) at the same time.
Standard rounding (mathematical rounding) rounds to the nearest value — if the decimal is 5 or higher, it rounds up, otherwise it rounds down. This is the most common method, and the one most people think of when they say "round".
Rounded down (floor) always rounds the number down to the nearest value, regardless of how large the decimal is. Rounded up (ceiling) does the opposite — always rounds up.
In practical calculations it's often wise to always round up, for example when working out how many packages of tiles or bags of gravel you need for a project — rounding down in such cases could leave you short of material.
Rounding (standard rounding) picks the nearest value based on the decimal. Rounding down means the number is always rounded downward, even if the decimal is high. Rounding up means the number is always rounded upward, even if the decimal is low.
This follows the "round half up" convention, which is the most common standard in math, spreadsheets and programming. If the number is exactly halfway between two values, it rounds up.
When you're working out how many units, packages or materials you need — for example tiles, paint or bags of gravel. Rounding down in such cases risks leaving you with too little.