If you add a .tm_properties file in your project folder, you can have TM set the tab size/type automatically based based on the source scope. For example adding the following:
[ 'source.c++, source.objc++' ]
tabSize = 3
softTabs = false
[ 'source.python' ]
tabSize = 4
softTabs = true
will indent all C++/Obj C++ files 3 spaces using hard tabs (softTabs = false), while python files will be indented with 4 spaces (softTabs = true). You can find the appropiate source scope by opening the file and using Shift-Ctrl-P. This will display all of the currently available scopes.