If you want to only add this charge for some items you can use:
TotalPrice = ([Price] + (([Title]!='' && ([Name]=='AUX-2000' || [Name] == 'AUX-2000X' || [Name] == 'AUX-2002' || [Name] == 'AUX-2002X'))?5:0)) * [Quantity]
or to exclude one use:
TotalPrice = ([Price] + (([Title]!="" && ([Name]!="AUX-2001"))?5:0)) * [Quantity]
This is done in the eCart dialog in the "Calculations" tab.