[Typo3-shop] Tax calculation incorrect?

[Robert Markula]

In our soon-to-be online shop the price without tax (PRICE_TOTAL_NO_TAX) 
is not calculated correctly.
We use these settings for the price calculation:
   TAXpercentage = 16.00
   TAXincluded = 1

Example:
When the total price (PRICE_TOTAL_TAX) is 10.00 euro, then the price 
without tax (PRICE_TOTAL_NO_TAX) is calculated as '8.62', but the 
correct amount would be '8.40' euro. The difference is 0.22 euro.

With a product that costs 1000 euro (PRICE_TOTAL_TAX), the 
PRICE_TOTAL_NO_TAX is calculated as 862.07 euro, but it should be 840 
euro. The difference of 22.07 euro is a bit more significant.

Is anyone else experiencing this? Where does this difference come from?

Regards,
Ro