I am also using e-cart5 and powerstore2.
I also did the currency modification from $ to euro. I used e-cart to display the euro at the checkout page, but it doesn't automatically change the $ symbol throughout the powerstore. In order to do this i had to change the $ symbol to the euro symbol manually at all the php pages of powerstore, (design mode and code mode). I had made a search at the forum for this issue and found a detailed explanation on how to do this. Try searcing "changing currency" at the forum search section. And i also think this issue is addressed at the product's how to documentation.