use strict;
use warnings;

use constant TO_US => 0.127;

while (<DATA>) {
    s/(\d+.\d+)/convert($1)/eg;
    print;
}

sub convert {
    return sprintf "%.2f", $_[0] * TO_US;
}


__DATA__
Hello all!  Today I bought breakfast for 02.50 and lunch for 10.20  Dinner was a real splurge at 21.00.