A solution that might lack elegance but should be pretty fast is a simple hash look-up. Construct a hash with keys running from 1 .. 100 and values equivalent to the 'probability' for each key. Something like this:

my $outcome = shift;

my %h = map { $_ => 10 * int ( ( $_ + 4 ) /10 ) } 8 .. 93;
@h{1 .. 3}    = (0)  x 3;
@h{4 .. 7}    = (5)  x 5;
@h{94 .. 97}  = (95) x 4;
@h{98 .. 100} = (99) x 3;

print defined $h{$outcome} ? sprintf "%02d\n", $h{$outcome} : 'ERROR';
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Update: Just realised that your numbers don't have to be integers. If so, change the beginning of the above to:

use POSIX;
my $outcome = ceil( shift );
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