Is anyone else having an issue with QB calculating the 5% GST on invoices incorrectly? Mine was off by 4 cents. But now my invoice doesn't match what I was paid.

I'm having the same issue. Simple multiplication operations should not have errors like this, especially in an accounting software.  

Hello will_ruetch-hotm,

Welcome to Community!  It' important to understand how QuickBooks calculates the sales tax on your forms.  I would be happy to provide some insight here!

When it comes to sales tax, you may note penny rounding, as the sales tax calculation is designed for 2 decimal place precision in QuickBooks Online.  Rate/Unit Price fields have a precision of 7 decimal places, whereas the Amount fields for each line have a precision of 2 decimal places.  Tax rounding is done per line.  Click here to learn more.

If you have any other questions, feel free to reach back out.  We would be glad to help!

I found the details on the significant digits per item and understand the rounding error. Why is tax not calculated on the subtotal value then? Would this not eliminate the rounding error? 

Hi DionJL,

To correct the rounding issue, you would need to manually adjust the line item, so it reflects in the sub total.  However, I do understand how this can affect your work, and for this reason I recommend submitting your feedback to our Development team.  Customer suggestions are greatly appreciated in assisting with improving your overall experience with QuickBooks Online.

Let us know if you have any other concerns.  We would be happy to assist!