The Salesforce system has the “Order Amount”(TotalAmount) order field - Salesforce calculate it’s value automatically as a sum of your OrderItems price
Unfortunately, Salesforce doesn’t provide the fields for additional order fees like: Shipping Const, Tax Amount and Discount price. This is the reason why the “Order Amount” value and Magento order Grand Total value could be different
Our Salesforce package added the following additional fields for the order:
tnw_mage_basic__Subtotal__c
tnw_mage_basic__Tax_Fee__c
tnw_mage_basic__Shipping_Fee__c
tnw_mage_basic__Discount__c
tnw_mage_basic__Grand_Total__c - this is formula field and value automatically as
tnw_mage_basic__Grand_Total__c = tnw_mage_basic__Subtotal__c + tnw_mage_basic__Tax_Fee__c + tnw_mage_basic__Shipping_Fee__c + tnw_mage_basic__Discount__c