Yes you do. 

You need an ABN as you are getting paid as a contractor not an employee. Deliveroo does not pay you a salary and wage like when you are employed as an employee. The difference is that when you are an employee tax is withheld from your salary by the employer. 

However this is not the case with Deliveroo, you are a contractor and Deliveroo pays you the amount of you earn from deliveries less a fee. There is no tax withheld on this payment and that is why you need to be registered as a business to ensure you are paying tax on this income.