How to round the number to the nearest ten?

[emazzu630]

With the button pressed (AP == 0), counting from 1 to 1 is performed with
the "UP and DOWN" buttons.
With the release button, (AP == 1), the count of 5 to 5 is performed
through the "UP and DOWN" buttons.
The point is that if the count of 1 to 1 is between 0 and 5 or between 5
and 10, the count of "5 to 5" is wrong.
A rounding is required that at the first pressing of the "UP and DOWN"
buttons, only the unit number will
"0" or "5" following the count of 5 to 5.
I declare the library "math.h" and tried unsuccessfully the
"value = ceil();" and "value = floor ();".
In the code below, I got the correct sequence on the display only to
appear when the button is pressed, when I release the number outside
the "0, 5, or 10" sequence appears again.
Anyone who has the solution, would you like to share? Thank you very much.

[Ttelmah]

What you are describing is 4/5 rounding. You do this with:

result=floor(val+4);

This gives 0 for 0,1,2,3,4, and then 5 for 5,6,7,8,9. Hence the '4/5'.

If you were working with floats, the formula is:

result=floor(val+4.99999);