You would need to customize the Order Total module for Low Order ot_loworderfee ...
You could change the code:
Code:
// calculate from flat fee or percentage
if (substr(MODULE_ORDER_TOTAL_LOWORDERFEE_FEE, -1) == '%') {
$low_order_fee = ((MODULE_ORDER_TOTAL_LOWORDERFEE_ORDER_UNDER - $order->info['subtotal']) * (MODULE_ORDER_TOTAL_LOWORDERFEE_FEE/100));
} else {
$low_order_fee = MODULE_ORDER_TOTAL_LOWORDERFEE_FEE;
}
NOTE: I did not test this with tax but it does produce the charge of $9.75 when set to 10% on orders set to less than 100.00 ...