public Double calculateTax(Id goodsSold, Account buyer){
  if(buyer.tax_exempt__c) {
    if(buyer.shippingState_taxed == true){
      if(goodsSold.price__c >= TAX_THRESHHOLD_LIMIT){
        return .85 * goodsSold.price__c;
      } else {
        return 0;
      }
    }
  } else {
    if(buyer.shippingState_taxed == true){
      if(goodsSold.price__c >= TAX_THRESHHOLD_LIMIT){
        return .85 * goodsSold.price__c;
      } else {
        return 0;
      }
    }
  }
}
