Tax Rate with 3 decimals rounding in invoices work bench

Hi All,

We got a new requirement for canada PST -QC where the tax rate has been changed from 9.5 to 9.975% w.e.f. 1st -jan -2013 , so when i give this in tax manager at rate level it shows 9.975.

But when i come to invoice workbench and also invoices which are interfaced through OM after the setup is all done and enterted an invoice here it is  showing the tax rate as 9.8 which is rounded from 9.975, and how do i avoid this rounding ? i want to show the complete 9.975 as tax rate ...as this may create a problem for tax calculation