Have you considered making use of the Aftership app, which does facilitate a connection with TNT and will allow you to track your shipments via that courier? Or were you looking for a more comprehensive, all round solution such as the ability to pull real time shipping rates through TNT directly?
Hope this helps and looking forward to your follow up!
You can check out the Multi Carrier Shipping Label app. Once you have the TNT account credentials and API keys, the integration with TNT can be easily done in the app.
Once this is done, you will be able to automate your shipping process. The app helps you generate the TNT shipping labels for all your orders in bulk. You can schedule pickup for your orders and also handle the tracking process with the app.