apply price changes to multiple forms

// http://www.gravityhelp.com/forums/topic/adding-taxes-to-total
add_action('gform_pre_render', 'add_surcharge_js');
function add_surcharge_js($form){

    // change the 9 here to your second form id.  Use as many form IDs as you want
    $formidscript = array(6,9);
    // if this form is not in our array of $formidscript, return $form info unchanged
    if(!in_array($form['id'], $formidscript))
    return $form;
    // otherwise, inject this script

    ?>
    <script type="text/javascript">
        function gform_product_total(formId, total){
            if(total == 0)
                return total;
            return total + (total * 0.039);
        }
    </script>
    <?php
    return $form;
}

add_filter("gform_product_info", "add_surcharge", 10, 3);
function add_surcharge($product_info, $form, $lead){

    // change the 9 here to your second form id.  Use as many form IDs as you want
    $formidcharge = array(6,9);
    // if this form is not in our array of $formidcharge, return $product_info unchanged
    if(!in_array($form['id'], $formidcharge))
        return $product_info;
    // otherwise, apply the price change to the front end

    $total = get_total($product_info);
    $fee = ($total * 0.039);
    $product_info["products"]["surcharge"] = array("name" => "Surcharge", "price" => $fee, "quantity" => 1);

    return $product_info;
}

function get_total($products) {
    $total = 0;
    foreach($products["products"] as $product){

        $price = GFCommon::to_number($product["price"]);
        if(isset($product["options"]) && is_array($product["options"])){
            foreach($product["options"] as $option){
                $price += GFCommon::to_number($option["price"]);
            }
        }
        $subtotal = floatval($product["quantity"]) * $price;
        $total += $subtotal;
    }
    $total += floatval($products["shipping"]["price"]);
    return $total;
}