There are two ways of calculating totals when it comes to invoicing.
Method 1: the sum of rounded values
Method 2: the sum of values, rounded
Zervant uses the Method 1. See below:
Method 1: Sum of rounded lines
For example, the sum of each line is 5.764, which is then rounded to 5.76 (2 d.p.). As such, the total of the invoice using method 1 is:
5.76 + 5.76 = 11.52
(Method 2: Sum of lines, rounded
5.764 + 5.764 = 11.528
Rounded to 11.53)