In the U.S., sales tax on digital products (games, DLC, downloadable content) is set state by state. Most states that levy a sales tax also tax digital goods, often through "marketplace facilitator" laws that make the store collect and remit the tax at checkout — so the price you see usually already includes it. A minority of states still exempt digital products. Your state's revenue authority (linked from the state pages) is the authoritative source for the current rate.
What this means for refunds: when a store approves a refund, it normally refunds the tax you paid too — you get the full amount back, not the pre-tax price. If your refund goes to Steam Wallet or store credit, the tax is typically returned to that balance as well. Check the specific platform policy for how it issues refunds (wallet vs. original payment method).
For a chargeback, the tax is part of the disputed amount — you dispute the full posted charge, tax included. If the platform later argues you "got the game," the tax component is part of why a chargeback fits best for unauthorized or misdescribed charges rather than simple change-of-mind; see the U.S. federal rights page for the fitting reasons.
If you believe you were taxed incorrectly (e.g., charged tax on a clearly exempt item, or tax on a refund you never received), that is a concrete, documentable error — exactly the kind your state AG or state tax authority can act on. Keep the order summary showing the tax line.