There is no specific information available indicating that Tata Motors will offer discounts on the Tata Nexon petrol variants exclusively during the Maha Navami festival. However, it is common for automobile manufacturers in India to offer festive season discounts and promotions around major festivals like Navratri and Dussehra. To find out about any potential discounts or offers, it would be best to check with local Tata dealerships or the official Tata Motors website during the festival period.