Rounding up/down of variables

As we are about to lose the penny in Canada, I need to know how to round up or down invoice amounts, which appear in, say, cell C25, i.e. =SUM(B5:B15). If the sum is $xx.01, or $xx.02, $xx.11 or $xx.12, etc., then the sum should be rounded down to $xx.00 or $xx.10, etc. If the sum is $xx.03 or $xx.04, $xx.13 or $xx.14, etc., then the sum should be rounded up to the next nickel. This I have accomplished by using CEILING, the problem is that the sums are always rounded up. Rounding down I have accomplished too, but the headache is with the in-between values, i.e.
If the sum in C25 equals 12.01 or 12.02 then the sum in C25 is 12.00, otherwise (else) the sum is 12.05.
If the sum in C25 equals 31.11 or 31.12 then the sum in C25 is 31.10, otherwise (else) the sum is 31.15. etc.

I don't know how to represent the variable in C25 and compare it with an unknown reference.

Any help or suggestion is greatly appreciated.
Thank you.
Quique

Originally Posted by martindwilson

use mround
=mround(c25,0.05)

Thank you very much for the help. As I look at the function, it seems sooo easy. It is exactly what I needed. The headache is gone and the "Aspirin" is back in the med cabinet. Now I have to figure out how to close the thread (I am a one-day newbie).

Again, thank you very much.

Quique