About AvaTax->

Global companies know that outsourcing key business functions like payroll and tax compliance makes good sense. Avalara AvaTax automates Value Added Tax (VAT) calculation directly within your accounting software. Whether your business is required to collect sales tax and/or VAT, manually calculating and filing tax in an ever-changing compliance environment can leave you exposed to audit risk.
With Avalara AvaTax your business is powered to handle global indirect tax situations and rules in the EU and beyond, including:

U.S. companies selling to EU companies or consumers.
Intra-EU Transactions.
EU companies selling to companies or consumers in the U.S.
EU companies with wholly owned subsidiaries in the U.S.

Reference from:- http://www.avalara.com

Below are the steps to install AvaTax in OpenERP

Step-1 Install Ava Tax Modules
Step-2 Setup > Installed Modules > Search for AvaTax. Click Install button
Step-3 Accounting > Configuration > AvaTax > AvaTax API. Click Create button
Step-4 Fill out the form with Company Code, Account Number and License Key provided to you by Avalara
Step-5 Accounting > Configuration > AvaTax > Exemption Code
Step-6 Accounting > Configuration > AvaTax > Product Tax Codes Add, remove and modify product tax codes
Step-7 Accounting > Configuration > AvaTax > Shipping Rate Configuration Add, remove and modify shipping methods and rates
Step-8 Accounting > Taxes > Taxes>Select AVATAX from the list view
Step-9 Sales > Configuration > Products > Product Categories Click Create button
Step-10 AvaTax Properties > Tax Code, Select the desired Tax Code
Step-11 Sales > Products > Products>Click Create button
Step-12 AvaTax Properties > Tax Code
Step-13 Sales > Customers>Click Create button
Step-14 Enter Customer Address Select the AvaTax tab>Click Validate button
Step-15 AvaTax Module will attempt to match the address you entered with a valid address in its database. Click the Accept button if the address is valid
Step-16 If the customer is Tax Exempt, uncheck the box Under Tax Exemption > Is Tax Exempt Select the desired Tax Exempt Code from the dropdown menu
Step-17 Accounting > Customers > Customer Invoices>Click Create button
Step-18 AVATAX Click Compute Taxes
Step-19 Validate Invoice>After the taxes have been computed click Validate button
Step-20 Register Payment>To complete the invoice click Register Payment button
Step-21 Complete the Pay Invoice window>Click Pay button to finalize the Customer Invoice
Step-22 Accounting > Customers > Customer Invoices>Select the invoice you wish to refund>Click Refund Invoice button
Step-23 Create Refund Invoice>Under Refund Method select Create a draft refund from the dropdown>Click Create Refund button
Step-24 You will be taken to the Customer Refunds list view
Step-25 Select the Customer Refund you wish to refund>Review the Draft Refund and click Validate button
Step-26 Click Register Payment button to complete refund
Step-27 Complete the Pay Refund window >Click Pay button to finalize the Customer Refund
Step-28 Create New Sales Order> Sales > Sales > Sales Orders
Step-29 AVATAX Click Compute in the subtotal section of the page