The first really good solution for navigation in Tunisia with cars is in this moment delivered from Sygic.
This soft has in this moment a nearly correct base of the streets, i tested it in the last 3 month.
It works properly on Galaxy S II, Galaxy Tab and Galaxy Tab 10.1 (P7500).
But please use this software in combination with your tablet or smartphone only with a bracket inside the car and not in your hand during driving!
Here is the site of the manufacture where you can buy your license and also download it from there. http://www.sygic.com/en/android:buy-now