@firefly – It appears that Digital River Ireland Limited are registered in Australia for GST:

https://abr.business.gov.au/SearchByAbn.aspx?abn=83053310056

That hardens the probability that the transaction, with its unexplained 10 percent surcharge, is being conducted under Australian jurisdiction, and therefore falls foul of the transparency requirements re price quotation and GST.

Regardless of legal requirements, it seems odd to me why any business would leave part of the bottom-line total of a transaction unitemised.