The currency format in the cart is set using the following line of code:
System.Globalization.NumberFormatInfo currencyFormat = new System.Globalization.CultureInfo(StoreSettings.StoreCurrency).NumberFormat;
Where "StoreSettings.StoreCurrency" is one of the following options you configure in the cart admin settings:
<asp:DropDownList runat="server" ID="ddlStoreCurrency" Width="200px" >
<asp:ListItem Value="en-US" Text="United States Dollar - $" />
<asp:ListItem Value="en-gb" Text="UK GBP - £" />
<asp:ListItem Value="fr-FR" Text="Euro - €" />
<asp:ListItem Value="en-za" Text="South Africa Rand - R" />
<asp:ListItem Value="en-za" Text="South Africa Rand - R" />
<asp:ListItem Value="zh-cn" Text="China" />
<asp:ListItem Value="da-DK" Text="Danish" />
</asp:DropDownList>
If you open up settings.ascx located in your \desktopmodules\smith.buynow folder and add the following list option to the currency dropdown it should give you what your looking for:
<asp:ListItem Value="en-IE" Text="Euro Ireland - €" />
Originally the cart used the localization setup in the web.config and server to set currency but alot of people had difficulty localizing their servers correctly especially if they were using shared hosting and the hosting company was in a different country so we created a currency setting in the cart admin settings where you could set the currency you wanted in the cart.