Tower Shield Specialist and Immediate Repositioning

Immediate Repositioning (Ex)
At 13th level, as an immediate action, a tower shield specialist can reposition his tower shield to another facing, but he cannot use this ability to interrupt an attack.

This ability replaces weapon training 3.

So if you get total cover for all attacks, do the attacks automatically hit your shield and cause damage?
Or is it simply a failed attack against the fighter?

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So if you get total cover for all attacks, do the attacks automatically hit your shield and cause damage?
Or is it simply a failed attack against the fighter?

depends on the attack result AND the type of attack

a touch attack can target the shield or user wielding the shield.

a melee attack needs to hit the shield or user(foe). Line of Attack issues for Ranged & melee thrown attacks. Not much of a problem for many magical attacks but you get a Reflex bonus and possibly evasion (the exact details when/how this happens and spell details will affect your bonuses).
Total Cover prevents making a melee attack on the wielder so it is against the shield. There's also CM Sunder. Realize that movement can cross the line of cover created by a tower shield. So battlefield control, having a shield wall, some special feats can prove very helpful.

I want to mention that exactly how that immediate action works, because there is an exception, for the Fighter-Shield Specialist is going to be subject to GM approval. I suspect that once an attack is declared you can't use it but CAN after the first iterative attack (but it needs to be declared 'early' with the first). You need to clarify exactly how this is going to work in your Home Game. Remember that it can use up your next swift action.