open(KEYS, "keys.txt") or die "error: $!";
open(VALS, "values.txt") or die "error: $!";
my ($key,$value);
my (%tips_by_name, %av_by_name, %max_by_name, %min_by_name);
while ($key=<KEYS>) {
    $value=<VALS>;
    chomp($key);
    chomp($value);
    $tips_by_name{$key} += $value;
    # code to do average, min, max here..
    # I'm not asking about that part, my question is
    # more about the way of reading files
}
close(VALS);
close(KEYS);
# code to print out the results here... again
# not part of my question at the moment.