Method of calculating and rounding values for Invoices

There are two options in the Invoices Templates section that help to avoid rounding issues with float numbers and missing cents:

1. Totals Calculation
2. Taxes Calculation

Let's review how they work with the following example, where the tax is 21%:

Item	Amount	Tax
Calls with the cost	$0.0050	$0.001050
Package #1 fee	$7.1144	$1.494024
Package #2 fee	$5.1144	$1.074024
Package #3 fee	$3.1144	$0.654024

Now, let's see how the calculations are made depending on the selected option:

1. Round then sum and Percent from the total amount

In this case, each line item is rounded first and then subtotal amount is calculated:

Item	Amount
Calls with the cost	$0.01
Package #1 fee	$7.11
Package #2 fee	$5.11
Package #3 fee	$3.11
Subtotal	$15.34

After that tax total and total due are calculated:

Item	Amount	Notes
Subtotal	$15.34
Tax total	$3.22	15.34 x 21%
Total due	$18.56	15.34 + 3.22

2. Sum then round and Sum of individual taxes

In this case, each line item and its taxes are added up first:

Item	Amount	Tax
Calls with the cost	$0.0050	$0.001050
Package #1 fee	$7.1144	$1.494024
Package #2 fee	$5.1144	$1.074024
Package #3 fee	$3.1144	$0.654024
Totals	$15.3482	$3.223122
Totals (rounded)	$15.35	$3.22

And then rounded results are used to calculate total due:

Item	Amount	Notes
Subtotal	$15.35
Tax total	$3.22
Total due	$18.57	15.35 + 3.22