There are many companies providing sales tax API. Out of all the companies, Avalara offers free API service for sales Tax. This gist is all about setting up avalara API and querying it.
The Free-To-Use API by avalara has some restrictions. Usage of this API is subject to rate limits. Users who exceed the rate limit will receive HTTP response code 429 - Too Many Requests. The requirement for this API is to create an avalara free trail account. You can create a free account using this link create free account.
Once you have filled the form from above link, you will get an e-mail containing temporary credentials to login the avalara account. The e-mail will look something like this:
