I'm not sure that's the same thing .
ti for ち, du for づ, zi for じ, zya for じゃ, tyu for ちゅ, etc is (to me, but it has been accepted otherwise) a different (if not wrong) adaptation of the so called heibon shiki (Hepburn roman transliteration/transcription). It is true that it is often found in Japan in latinized names of shops, brands etc written by graphists who don't know much about official transcription.
Be it as it may, hanbunn , or any ending with an,in,un,en,on won't have a double n at the end, whatever the transcription standard adopted, that's what I dare think.