How do I handle tax calculations with discounts?

As an e-commerce business owner, I'm struggling to understand how tax calculations should work when applying discounts to products. I want to ensure I'm complying with tax regulations, maintaining accurate financial records, and providing transparent pricing to my customers. There are so many variables to consider - do discounts apply before or after tax? How do different jurisdictions handle tax calculations with promotional pricing? I need a comprehensive strategy that works across multiple sales channels and keeps my accounting clean and compliant.