Need to add sales tax for single state

1

working on an as3 checkout cart in flex…anyone have suggestion on how to do sales tax for one state? ie california. thx a lot

private function doDirectPayment():void
            {
                paymentButton.enabled = false;
                
                params = new Object();  
                
                params["PAYMENTACTION"] = "Sale";
                params["CURRENCYCODE"] = "USD";
                 params["AMT"] = (ProductsView(parentDocument).cartPanel.total + (ProductsView(parentDocument).cartPanel.numProducts * ProductsView(parentDocument).cartPanel.shipping));
                 params["ITEMAMT"] = ProductsView(parentDocument).cartPanel.total;
                 params["SHIPPINGAMT"] = (ProductsView(parentDocument).cartPanel.numProducts * ProductsView(parentDocument).cartPanel.shipping);
                 
                                
                 params["FIRSTNAME"] = firstName.text;
                 params["LASTNAME"] = lastName.text;
                 params["STREET"] = address.text;
                 params["STREET2"] = address2.text;
                 params["CITY"] = city.text;
                 params["STATE"] = String(regions.selectedItem.@code);
                 params["ZIP"] = zipCode.text;
                 params["PHONENUM"] = phone.text;
                 params["EMAIL"] = eMail.text;
                 params["COUNTRYCODE"] = String(countries.selectedItem.@code);    
                              
                 params["SHIPTONAME"] = shippingName.text;
                 params["SHIPTOSTREET"] = shippingAddress.text;
                 params["SHIPTOSTREET2"] = shippingAddress2.text;
                 params["SHIPTOCITY"] = shippingCity.text;
                 params["SHIPTOSTATE"] = String(shippingRegions.selectedItem.@code);
                 params["SHIPTOZIP"] = shippingZipCode.text;
                 params["SHIPTOCOUNTRYCODE"] = String(shippingCountries.selectedItem.@code);
                 params["SHIPTOPHONENUM"] = shippingPhone.text;

grabbing state/country info from xml

<country name=“United States of America” code=“US”>
<state code=“AL”>Alabama</state>