After a bit more googling i found the answer:

dataless <dataless767@hotmail.com> wrote in article
<a8liar$m91$1@helle.btinternet.com>...
> Hi all,
> Can anyone recommend an algorithm to round an integer to the nearest
+ 5 or
> 10?


Let's round n to the nearest five first:

Divide n by 5
Add 0.5 to n
Discard the fractional part of n
Multiply n by 5

Now let's round to the nearest ten:

Divide n by 10
Add 0.5 to n
Discard the fractional part of n
Multiply n by 10


Now let's round to the nearest seven:

Divide n by 7
Add 0.5 to n
Discard the fractional part of n
Multiply n by 7


Do you see a pattern?

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or in perl

#!/usr/bin/perl -w

use strict;

my $prec   = 5;
my $number = 32;

$\="\n";

print int(($number/$prec)+.5)*$prec;
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smaller, anyone?