For quoting direct speech, American rules place periods and commas inside the quotation marks all the time. In fiction, both styles are the same. In non-fiction, British publishers may permit placing punctuation that is not part of the person’s speech inside the quotation marks but prefer that it be placed outside. According to the "Cambridge Handbook for Editors, Copy-editors and Proofreaders", periods and commas that "are" part of the person’s speech are permitted inside the quotation marks regardless.