Invoice total with tax inclusive prices

We have set up the plugin with Tax Inclusive prices (Australian GST, 10%) and this works some of the time. However, in many cases the total invoice amount (including tax) is different to the total of the gross prices. For example, a product with a price of $27 inclusive is invoiced at $27.01

This occurs because the tax free price is calculated to be $24.55 and tax on that is $2.46 (both after rounding).

If 2 of these products are purchased, the amount charged is $54.01, again incorrect.

Going further, even though buying one product for $18 works OK, buying 2 of them results in an invoice total of $35.99

In summary, the invoice total has to be calculated using the tax included prices. The code refers to this problem and specifically stores the gross price...

// store orignal price
// if tax_inclusive==true, before_tax_price() rounds to two decimal places
// the original price cannot be accurately calculated on the order tracking page with just the before_tax_price value
$filtered_cart[$product_id][$variation]['price_db'] = $data['price'];

However, this original price is not referenced anywhere in the code.

Even though I have spent hours trying to patch the code to overcome this, I have not had success. We urgently need a fix for this please.

Looking forward to your help, Nigel