Here's a little toy to examine just what's going on here. Try it out and play with the ranges.

#!/usr/bin/perl -w
use strict;
require Math::BigFloat;


my $sig = $ARGV[0] || 2;
my $ini = $ARGV[1] || 0; 
my $end = $ARGV[2] || 1;
my $inc = $ARGV[3] || 0.0001;

test_methods($sig,   $ini, $end, $inc);

sub test_methods {
    my ($sig, $ini, $end, $inc) = @_;
    my $count = 0;
    my %result = ();

    print "For $ini to $end, incrementing by $inc, with $sig significa
+nt digit". ($sig==1 ? '' : 's') ."\n";

    for (my $num = $ini;$num<$end;$num += $inc) {
        $count++;
        $result{'real'} += $num;
        $result{'ffround'} += Math::BigFloat->new($num)->ffround( -$si
+g );
        $result{'sprintf'} += sprintf "%0.${sig}f", $num;
        printf "%-20s || %-10s || %-20s\r", ($result{'real'}/$count), 
+($result{'ffround'}/$count), ($result{'sprintf'}/$count);
    }
    print ' 'x58 . "\rOver $count iterations:\n";

    print "   Method |         Sum         | Average\n";
    
    for (qw[real ffround sprintf]) {
        printf "%9s | %-20s| %-20s\n", $_, $result{$_}, ($result{$_}/$
+count);
    }

    return \%result;
}
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