As far as a I know, there is no mention of retail invoice. GST rules are being revised and keep revising until GST is implemented.
Under GST its called tax invoice and format of tax invoice can be download from this link.
You can use the invoicing application of knowyourgst for generating online invoice for your business.
Benefits of knowyourgst invoicing application are:
- It is online so you can access from anywhere.
- You do not have to send any data to your auditor for uploading sales details, just give him user id and password. He can download the data in excel to upload it to GST portal.
- It is amazingly fast and never puts you in trouble.
- Highly secured.