No, they can't. They can force you to let them try to open it, but they can't force you to open it for them.
If you have some mechanism like "if you try to open this incorrectly it destroys the contents", and you intentionally don't disclose that with the expectation that they're going to try and fail and destroy the contents, you might get charged with destruction of evidence.
(EDIT: Replies suggest that disclosure may not suffice.)