The authors of the spec made some provisions, and very likely all of them are useful and correct, the issue is how the programmers will use them, and in some cases there isn't even a "correct" solution that everyone uses.

A classic example in invoicing is an item that is advertised for 60.00 (to the final user) VAT 10% included.

If you try making an invoice for that sum in a few programs you will find three or four way it is implemented.

Some will have 54.54+5.45=59.99, some will have 54.54+5.46=60.00, some will have 54.55+5.46=60.01 (and possibly a "discount" of 0.01), some will have 54.545+5.45=60.00, some will have 54.54545454+5.45=60,00.