Your made yourself clear enough in the OP but you don't seem to like the answers (or won't understand them?).
The numbers in your latest post, 30, 23, and 13, happen to be what I gather your mean by a "nice" case; that is, when calculated as percentages of their total and rounded, the percentages add up (nicely) to 100.
Here's a case where the numbers are not "nice" and where a disclaimer is the only reasonable solution (fudging is NOT, IMO, reasonable):
#!/usr/bin/perl
use strict;
use warnings;
#785290
my $Google=30; my $Yahoo=23; my $Bing=12;
my $sum=$Google + $Yahoo + $Bing;
my $google_percent = $Google/$sum;
print "G: $google_percent";
my $yahoo_percent = $Yahoo/$sum;
print "\tY: $yahoo_percent";
my $bing_percent = $Bing/$sum;
print "\tB: $bing_percent \n";
my $total = ($google_percent + $yahoo_percent + $bing_percent);
my $roundedG = sprintf("%.2f", $google_percent);
my $roundedY = sprintf("%.2f", $yahoo_percent);
my $roundedB = sprintf("%.2f", $bing_percent);
my $rounded = sprintf("%.2f", $total);
print "Google: $roundedG; Yahoo: $roundedY; Bing: $roundedB; Total: $r
+ounded \n";
printf ('%.0f', (($Google/$sum)*100));
print "%\n";
printf ('%.0f', (($Yahoo/$sum)*100));
print "%\n";
printf ('%.0f', (($Bing/$sum)*100));
print "%\n";
print $rounded*100 . "% (Percentages may not add up to 100 because of
+rounding errors!)\n";
