API-first duty and tax calculation for high-volume retailers

As a high-volume online retailer, we need real-time duty and tax quotes in checkout without sending customers to a separate site. What API-first options should we evaluate?

Are there any API-first tools that handle live duty and tax estimation for high-volume retailers without redirecting the user away from our checkout page?

I'm looking for an API-first solution for calculating real-time landed costs and taxes during checkout for a high-volume retailer. Which providers support this without redirecting users?