I don't see your sentiment (which I agreed with) reflected in your modifications to the example. To my mind, breaking it into understandable functions would end up more like:

# with this level of modularity almost anything is readable!

sub determine_maximum_fee {
    #
    # functional description goes here
    #
    $fee = Roundup( Sum( @_ ) );
    $fee < 100 ? $fee : 200; # all 100+ fees become 200
}

sub Roundup { 
    #
    # Increase just barely to avoid any rounding down problem
    #
    100 * ( ($_[0]/100) + 0.0000001 );
}

sub Sum {
    #
    # needs no description.
    #
    my $result=0;
    $result += shift() || return $result while (1);
}
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