Punctuations and Closing Quotation Mark

I prefer placing punctuation next to the closing quotation mark like this:
I'm watching "Titanic".

However, when there is already a punctuation within the quote, is it right to add another punctuation after the quote?
Did you say "Hello?"?
No, I didn't say "Hello?".
Then did you say "Hello."?
Yes, I said "Hello.".
A punctuation, before the closing quotation mark, for the quoted sentence. And another one, after the mark, for the main sentence. It might have made sense, if only I have ever seen such usage. (Especially the last one, which contains two full stops. It looks so wrong.)

Answer

This is a matter of style. Consult your style guide, either the one you've adopted or the one thrust upon you. I use The Chicago Manual of Style:

When two different marks of punctuation are called for at the same
location in a sentence, the stronger mark only is retained.

Example:

Who shouted, "Up the establishment!"

The question mark that ordinarily appears at the end of an interrogatory is omitted. I infer from this rule the following:

Who said, "Up the establishment"?

The exception is a period that ends an abbreviation, which is retained thus:

He said, "I don't work for Dewey, Cheatham and Howe, Ltd."!

unless it abuts a period that ends a sentence:

I don't work for Dewey, Cheatham and Howe, Ltd.