THAT’S A GOOD ONE can mean you liked a joke or it can mean you don’t believe what is said.
That’s a good one. You tell great jokes.
You met Justin Timberlake? That’s a good one. I don’t believe a word
THAT’S THAT means that things are decided and finished.
No more discussions. I have decided and that’s that.
I am not going to give you any money and that’s that.
THAT TAKES CARE OF THAT means that you have finished dealing with something.
That takes care of that. We can put away all the files
I have spent all day dealing with this problem but I have solved it. That takes care of that.