Grammatically Correct: The writer's essential guide to punctuation ...

PUNCTUATION
• It is permissible to use a pair of dashes within parentheses, but
think before you do so. The parenthesized text is already an aside,
and it can be distracting to have an aside within an aside. (See
"Marking Off a Descriptive Element or Digression" on page 154.)
• Ensure that parentheses always come in pairs. Particularly with
longer elements, writers occasionally forget that text is parenthetical,
and neglect to close it off.
• When parentheses enclose a sentence that stands alone, put
the terminal punctuation mark inside the parentheses.
Dealing with multiple punctuation marks in a single sentence can be
tricky. (The positioning of parentheses and periods is a case in point.)
The shoe was now on the other foot. (Or was it?)
For weeks afterward, he kept a wide berth of the shop. (Evidently, he had
learned his lesson!)
• When parentheses enclose just part of a sentence, obsenre the
following conventions:
-Put the terminal punctuation mark outside the parentheses,
even if the parenthesized element comes at the end.
The promotion was unanimously approved (although some members
privately had their doubts).
Do you really think this move is necessary (because if not, we still have
time to cancel it)?
After all, someone has to win (ridiculous as the odds are)!
(In the case of exclamation points, note that it would actually be
somewhat counterproductive to put parenthesized text at the end
of the sentence, since the purpose of an exclamation point is to
impart excitement or urgency, and the interruption would detract
from this. If you ever do construct such a sentence, analyze it
carefully. It is likely that recasting it would improve it.)
-If a comma, semicolon or colon is needed between what
precedes and follows the parentheses, put it after the closing
parenthesis-not before the opening one, and not in both places.
The room contained only a sofa (much the worse for wear), a faded
armchair and a carpet (if that stained and threadbare square could be
called such); the other furnishings had long since been sold off.
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