If you're in the US or Canada, Avalara is a solid solution. They offer sales tax calculation and filing (in some states) and integrate into the popular shopping

If you're in the US or Canada, Avalara is a solid solution. They offer sales tax calculation and filing (in some states) and integrate into the popular shopping carts/accounting software. The agency I work at has done numerous implementations for large online retailers. Last I checked pricing was at $350/yr for up to 700 transactions.