It is possible to import Sub Total Lines in Invoices / Estimates using SaasAnt Transactions (Online).
How to import Sub Total Lines ?
Kindly map one of your file column to "Show Sub Total" field and fill with values like "TRUE" , "T" , "YES" or "Y".
The particular row which has "Show Sub Total" should have the information like below image
It will be reflected in QuickBooks as below