Taken from FAQ portion on their website:
Do you have seperate charges even if I bid on 
items from the same seller? 
 
All auctions are treated seperately, regardless 
of the fact they may be from the same seller. 
Rinkya's system is automated and cannot 
recognize auctions that may be from same 
sellers. We hope to provide a more intuitive 
system in the future that can recognize same 
seller auctions.
Here's the URL:
http://www.rinkya.com/newsite/faq_url.php