I have the same problem - it's very frustrating.
I raise an invoice with unit prices of 0.008 but these are rounded up to 0.01 on the invoice. I end up with line entries like this:
Widgets 50,000 @ 0.01 = Â£400
Obviously this looks bad when invoicing clients as the maths is just wrong and I have to put a note on the invoice explaining my account system isn't capable of more than 2 decimal places, but that the correct amount is 0.008 per unit.
There's a further bug that if you then go back and edit the invoice the gross amounts are recalculated so what should have been 50,000 x 0.008 =Â£400 but shows as 50,000 x 0.01 = Â£400 on a pdf is then changed to 50,000 x 0.01 = Â£500 - if you print out the pdf again you end up charging 0.01 and not 0.008.
If I have a large invoice and need to add items or make a small adjustment I then have to go back to every line item and re-adjust from 0.01 to 0.008. I missed this one an invoice to a client and accidentally over billed them - this caused problems with the client.