Explanation of the approach BarBooks takes when calculating GST on invoices
BarBooks takes a Line item approach which calculates tax on a per line basis, rounding to two decimal places, and then sums the tax totals of each line to calculate the total invoice tax, this explains why you may view a discrepancy when you take the excl GST amount, divide by 10 and compare to the GST BarBooks calculates. This is an acceptable approach by the Australia Tax Office and which is employed with other software platforms such as Xero. The main reason is that it provides us with greater flexibility in our service offering.
But should your customers require the exact 10% as the GST amount. You may reprice the invoice.
Open the Invoice > Click the Discount button > Select Reprice > enter the Incl GST amount on the field.