You use the expression 'without replying tentative'. I can imagine that you want to reply and tell the meeting organiser that you declined the invite, but still show it on your calendar.
If the reply is the issue, then when you receive the invitation, decline it and send a response as usual. Then find the meeting request in your deleted items folder, and accept it as tentative. Choose 'Do Not Send A Response'.
This way, the meeting will be added to your calendar, but the organiser will be told that you have declined the meeting.