In this very case the .dep list of the keepassx.tcz extension in 2.x repo might help as an approxymate indication.
NACKAs 'keepassx.tcz.dep' in the 2.x repository contains:
' Xlibs_support' which is not in TC 3.x (well, it's replacement would be 'Xorg-7.5-lib'),
'qt-4.5-base', which has been replaced by 'qt-4.x-base',
and the other two extentions are now indirect dependencies
All that indicates to me that this particualr .dep file predates the introduction of recursive dependencies. Therefore it's not an ideal base to guide on towards a "proper" dependency file. And with "proper" I mean to include all what's really required and no redundant entries.