Tower Shield Proficiency page at d20pfsrd says:
Benefit: When you use a tower shield, the shield's armor check penalty only applies to Strength and Dexterity-based skills.
Normal: A character using a shield with which he is not proficient takes the shield's armor check penalty on attack rolls and on all skill checks that involve moving, including Ride.
Create a Dwarf Cleric with 10 Strength and Tower Shield Proficiency; tower shield and club equipped. His BAB is +0, Str bonus +0, so his overall 1H-P bonus should be +0. However, there is a "Misc" -2 penalty applied which goes away if you unequip the tower shield.
Since he has Tower Shield Proficiency, there should be no To Hit penalty for using the shield.
You might want to read the Paizo PRD (http://paizo.com/pathfinderRPG/prd/equipment.html#shield-tower):
Shield, Tower: This massive wooden shield is nearly as tall as you are. In most situations, it provides the indicated shield bonus to your AC. As a standard action, however, you can use a tower shield to grant you total cover until the beginning of your next turn. When using a tower shield in this way, you must choose one edge of your space. That edge is treated as a solid wall for attacks targeting you only. You gain total cover for attacks that pass through this edge and no cover for attacks that do not pass through this edge (see Combat). The shield does not, however, provide cover against targeted spells; a spellcaster can cast a spell on you by targeting the shield you are holding. You cannot bash with a tower shield, nor can you use your shield hand for anything else.
When employing a tower shield in combat, you take a –2 penalty on attack rolls because of the shield's encumbrance.
In a nutshell, instead of a -12 to hit, you only get -2 to hit.
The official rules are pretty clear, the -2 to hit is Encumbrance based, not Armor Check Penalty based.
Thanks for the quick response. Much appreciated.