If you tag a commit you better stick to your guns and never change it. You can't just re-tag or re-roll your releases because you found a bug. Bugs happen. Increment your version number, cut/tag a new release, and move on. You will never have a perfect release. Ever.
If you create a php-7.0.0 tag, and you find a bad bug, then make a new tag, either php-7.0.1, or since you might still want to call the release PHP 7.0.0, maybe name it php-7.0.0-bugfix1 or something.