To do your return for you? Or to do their own return? NO, not to do their return.
The Online version is only good for 1 return. But you can use the same email address for 5 accounts. To do another return log out of your account and set up a new account and new user name and pay any fees again. That's why it's better to use the Desktop CD/Download program. The Desktop program can do more than 1 return and efile 5 for free.
How to start another return in the Online version
If you have already completed and filed your tax return, NO.
The TurboTax online editions can only be used to complete one tax return per account and User ID.
Start another tax return using the online editions a new account would have to be created with a new User ID - https://turbotax.intuit.com/personal-taxes/online/