Hi,
That feature comes with our all VM Templates, and works flawlessly.
But It doesn't work properly in modules when different scenarios involves (due to TAX rule or Discount rule - some people use the general discount rule, some people use "discount per product" etc..) so; we decided to exclude this feature from our VM modules, because it just doesn't work in all cases (which i believe is the same reason why Virtuemart official module also not support it)
Regards.