Hi Robert,
I just tested this on 6.78 and the [GSTINCL] is working correctly for me when using the VAT/GST (Product Inclusive) Tax Method (see attached screenshots below).
I would like to have you login to one of our public test portals and configure the cart the way you have your's configured and try to replicate the issue. This will determine if the issue you are reporting is with the latest version of the cart or an issue with your specific DNN portal/cart install. Please use the following link to submit a Help Desk ticket so we can provide you with credentials to login to the test portal:
http://helpdesk.smith-consulting.com/...