Write a definition of rounding in your own

Rounding is when you have at least a two digit number (26 for example) and if the number the right (6) is 5 or above  then the number goes up one unit, (therefore 26 becomes 27). But if the number (22) to the right is 4 or lower, then the number to the right stays the same, but the number to the right becomes a zero, (making 22 now 20).

What are the following algebraic equations. you need to post those if you want the answer