Dynamics AX Extension Development

Need to develop Dynamics AX extension to connect to JSON web service API. The extension is to incorporate automated tax solution to calculate taxes from within Dynamics AX application. We have client who wants to calculate taxes on invoices in Dynamics AX, we found web service and now we trying to develop an extension that connects to the web service. Experience in developing Dynamics AX extensions is a must. Do you have previous experience with developing Dynamics AX extensions? Please explain.