hook_calculate_tax

document say Each line item is an associative array containing the tax's id, name, amount, and weight. but it not work. I look at this code

function uc_line_item_tax($op, $order) {
  switch ($op) {
    case 'load':
      $lines = array();
      $taxes = uc_taxes_calculate($order);
      foreach ($taxes as $tax) {
        $lines[] = array(
          'id' => 'tax',
          'title' => $tax->name,
          'amount' => $tax->amount,
          'weight' => variable_get('uc_li_tax_weight', 9) + $tax->weight / 10,
          'data' => $tax->data,
        );
      }
      return $lines;
  }
}

so my_calculate_tax return a object . it is work.