How do you create a tax debit in a sales invoice

I have to issue invoices with the retail value of the sale and apply a commission to the recipient so that they just pay the net amount.

With Reckon Hosted, I wish to track the sale as GST and the Commission as NCG.

Thus the tax report would show gross sales plus GST and Commission plus GST.

Correct reporting of sales and commission.

Many thanks 

John