Here's the story. If they offer you to pay in your home country, the only time you should do it is if your credit card charges more than a 3% foreign transaction fee. When you select to pay in your home currency, you will have to sign 2 cc slips. One of them is for the currency conversion and it says in small print on this slip that they are charging a 3% fee.
The first time it was offered to me, I asked the SA if there was any difference or fee...I was told "no". Then I read the little slip and was livid.
If your card charges more than 3%, it would be worth it. If not, stick to local currency..
Totally agree with this, when out of my home country, I used a foreign transaction fee free card so it always works out best for me with local currency.
Happy shopping!