[DUG] MYOB Rounding Issue - MYOB Data File Attached

[Paul Heinz]

Hi Cheng Wei 

> Please find attached a zip file containing:
>  
> - A company data file (AccountRight Enterprice v19+);
> - A sample invoice pdf generated by our system;
> - An MYOB Item Sales import file generated by our system, 
> containing line items of the invoice.
> 
> Invoice Number: GR2115

Very interesting. As it turns out, from that invoice it would appear
that MYOB uses the same GST rounding model that we use in our product,
Accredo.

Our algorithm is a line-by-line GST calculation rounding to nearest BUT
with flowthrough accumulated roundoff. The result of this algorithm is
that you get exact whole cents on each line which is ideal for
accounting analysis but the resulting total GST is also consistent with
rounding the whole document total just once.

To get an idea of how this algorithm works on a line by line basis:

The 1st line is $272.16, add 15% = $312.894, rounds to $312.89 and 0.004
difference.

The 2nd line is $28.88, add 15% = $33.212 + 0.004 diff = $33.216, rounds
to 33.22 and -0.004 difference.

The 3rd line is $80.00, add 15% = $92.00 - 0.004 diff = $91.996, rounds
to $92.00 and -0.004 difference.

The 4th line is $589.50, add 15% = $677.925 - 0.004 diff = $677.921,
rounds to $677.92 and +.001 difference.

The 5th line is $58.95, add 15% = $67.7925 + 0.001 diff = $67.7935,
rounds to $67.79 and +0.0035 difference.

The 6th line is $60.55, add 15% = $69.6325 + 0.0035 diff = $69.636,
rounds to $69.64 and -0.004 difference.

The overall GST total = $163.51.

Note that this result is the same as taking $1090.04, add 15% =
$1253.546, rounds to $1254.55 and -0.004 difference.

In each of the above examples, I'm showing the inclusive total which is
how MYOB stores it per invoice line but you can also just calculate GST
at 15% and round that with the flowthrough model which is what Accredo
does since they are mathematically equivalent.

I'm not sure if MYOB also handles negative documents consistently and
rounds exact half cents _down_ for credits which is something we also
factor into the algorithm in Accredo. 

We like our negative invoices to give the exact same figures as an
equivalent positive invoice with just the signs flipped. If you use
standard IEEE round-to-nearest, you won't get that for documents with
lines that have exact half cents of GST.

I'd need an example of an equivalent credit document to confirm MYOB's
behaviour in that case.

Cheers,
  Paul.