TAX Rate Change Increment Upwards? (VAT)

[shaky]

Here is the problem:

 

If I have an item worth ?1.40 Oscommerce then adds 17.5% VAT (UK TAX RATE) and the item now shows as being ?1.64.

 

But my accounting package interprets ?1.40 as being ?1.65 with the VAT.

 

 

This is because:

 

1.40 x 17.5 / 100 = 1.645

 

 

Basically:

 

Oscommerce interprets any item with the Tax Rate below 1.645 as 1.64 but my accounting package interprets it out as being 1.65.

 

How can I tell Oscommerce that any item with a figure of 0.005 to increment this upwards to the next decimal?

 

Many thanks :):)