That's all vs. That's it?

[yamyam]

Hello, teachers.

I'm wondering which is correct for the replies to questions, "That's all" or "That's it," in the following cases.
Would you give any hint for the usage?

1. A waiter or a waitress at a restaurant says to you, "Anything else?"
2. A salesclerk at a shop says to you, "Anything else?"

Is there any big difference in meaning between them?
Does the difference occurs according to situations?

I hope you'll help me with this!
yam

 

[bhaisahab]

"That's all, thank you" works for me.

 

[riquecohen]

Both work for me, followed by "thank you." "No, thank you" is also appropriate.