Hi Simonexc,
I appreciate you reaching out here, with regards to your sales tax in QuickBooks SDK. However, I feel you would benefit from contacting us outside of Community for personal assistance. Our QuickBooks Desktop specialists would be happy to work with you in real-time and ensure you're able to accomplish your QuickBooks goals as soon as possible!
If you have any other questions, feel free to reach back out. We'd be happy to help!