Wrong Tax

The sum of the total tax(56.87) is wrong.

19.25 + 37.02 = 56.27, not 56.87

README.md

@@ -320,7 +320,7 @@ The `ZugferdDocumentBuilder` class is again the central entry point to generate
     ->setDocumentBuyerAddress("Kundenstraße 15", "", "", "69876", "Frankfurt", "DE")
     ->addDocumentTax("S", "VAT", 275.0, 19.25, 7.0)
     ->addDocumentTax("S", "VAT", 198.0, 37.02, 19.0)
-    ->setDocumentSummation(529.87, 529.87, 473.00, 0.0, 0.0, 473.00, 56.87, null, 0.0)
+    ->setDocumentSummation(529.87, 529.87, 473.00, 0.0, 0.0, 473.00, 56.27, null, 0.0)
     ->addDocumentPaymentTerm("Zahlbar innerhalb 30 Tagen netto bis 04.04.2018, 3% Skonto innerhalb 10 Tagen bis 15.03.2018")
     ->addNewPosition("1")
     ->setDocumentPositionProductDetails("Trennblätter A4", "", "TB100A4", null, "0160", "4012345001235")
@@ -366,7 +366,7 @@ Use the class ```ZugferdDocumentPdfBuilder``` if you already have an existing pr
     ->setDocumentBuyerAddress("Kundenstraße 15", "", "", "69876", "Frankfurt", "DE")
     ->addDocumentTax("S", "VAT", 275.0, 19.25, 7.0)
     ->addDocumentTax("S", "VAT", 198.0, 37.02, 19.0)
-    ->setDocumentSummation(529.87, 529.87, 473.00, 0.0, 0.0, 473.00, 56.87, null, 0.0)
+    ->setDocumentSummation(529.87, 529.87, 473.00, 0.0, 0.0, 473.00, 56.27, null, 0.0)
     ->addDocumentPaymentTerm("Zahlbar innerhalb 30 Tagen netto bis 04.04.2018, 3% Skonto innerhalb 10 Tagen bis 15.03.2018")
     ->addNewPosition("1")
     ->setDocumentPositionProductDetails("Trennblätter A4", "", "TB100A4", null, "0160", "4012345001235")
@@ -428,4 +428,4 @@ $mergeToPdf = dirname(__FILE__) . "/fullpdf.pdf";
 
 ### Validation
 
-This library offers several options for checking and validating a document. Please visit the corresponding page in our [Wiki](https://github.com/horstoeko/zugferd/wiki/Validation).
+This library offers several options for checking and validating a document. Please visit the corresponding page in our [Wiki](https://github.com/horstoeko/zugferd/wiki/Validation).