Problem with tax calculation - can somebody confirm it?

[custompresta]

The tax is calculated wrong, depending on the product quantity.

Sample 1:
Product incl. 19% tax = 13.48
Cart quantity 6
Total incl. tax = 80.88
Tax in Cart = 12.90
Total excl. tax in cart = 67.98

But must be:
Tax in Cart = 12.91
(80.88 / 119 * 19) = 12.9136
Total excl. tax in cart = 67.97
(80.88 / 119 * 100) = 67.9663
Total incl. tax in cart = 80.88
(12.9136 + 67.9663) = 80.8799

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Sample 2:
Product incl. 19% tax = 13.48
Cart quantity 5
Total incl. tax = 67.40
Tax in Cart = 10.75
Total excl. tax in cart = 56.65

But must be:
Tax in Cart = 10.76
(67.40 / 119 * 19) = 10.7613
Total excl. tax in cart = 56.64
(67.40 / 119 * 100) = 56.6386
Total incl. tax in cart = 67.40
(10.7613 + 56.6386) = 67.3999

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Sample 3:
Product incl. 19% tax = 13.48
Cart quantity 4
Total incl. tax = 53.92
Tax in Cart = 8.60
Total excl. tax in cart = 45.32

But must be:
Tax in Cart = 8.61
(53.92 / 119 * 19) = 8.6090
Total excl. tax in cart = 45.31
(53.92 / 119 * 100) = 45.3109
Total incl. tax in cart = 53.92
(8.6090 + 45.3109) = 53.9199

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So as you can see, the total incl. tax is right. But the total excl. tax and the the tax itself is wrong calculated.

And here is a right calculated one, with 2 products in cart.
It also is correct with 1 product in cart.

Sample 4:
Product incl. 19% tax = 13.48
Cart quantity 2
Total incl. tax = 26.96
Tax in Cart = 4.30
Total excl. tax in cart = 22.66

This is calculated right:
Tax in Cart = 4.30
(26.96 / 119 * 19) = 4.3045
Total excl. tax in cart = 22.66
(26.96 / 119 * 100) = 22.6554
Total incl. tax in cart = 26.96
(4.3045 + 22.6554) = 26.9599