How tax routes:
- Region = Local → CGST + SGST (50/50 split). Central → IGST (full rate). Driven by the TaxCategory percentage on each item.
- Transaction Type = Stock Transfer or Import → forces 0% tax on the entire transaction (ignores item's TaxCategory). Other runs normal Region split.
- No Tax Posting = report-filter flag only. Doesn't affect tax math — for filtering rows in reports.
- Reverse Charge = buyer pays GST instead of seller (B2B GTA, lawyer fees, import services).