gistfile1.php

<?php

class CustomCommerceTax {
  $this->_aItems;
  $this->_aShipping;
  $this->_aCoupon;
  
  public function __construct($aItems, $aShipping, $aCoupon) {
    $this->_aItems = $aItems;
    $this->_aShipping = $aShipping;
    $this->_aCoupon = $aCoupon;
  }
  
  public function CalcluateTax() {
    // API calls here
    // Access shipping/coupon/items: $this->_aItems
  }
  
  public function EstimateTax() {
    // API calls here
    // Access shipping/coupon/items: $this->_aItems
  }
}