Invoice Total Issues

[Jour]

We have a similar issue, everything has been running fine except for the latest order that we received.

The sub-totals are all correct and as follows;
Sub-Total: $363.54
Postage: $14.00
Group Discount: - $51.92
Quantity Discount: -$72.71
GST Tax: $21.90 (this amount is already calculated in totals)
Total: $240.49 - this amount should be $252.90

There is a diference of $12.42 which, not sure why.

There is nothing else unusual about this order, we have had previous orders with discounts etc and everything was fine.

Does anyone have any ideas what could be causing this?

(screenshot attached)

thanks.

www.jour.com.au