decimal places

I would like to see a separate setting for decimal places for item prices.

Currently we buy and sell in grams, the prices being calculated to 6 decimal places.

We sell in another currency (USD), so would like the final price to be calculated to 2 decimal places.

I would like to see the "Price after tax" column in a sales invoice separately configurable from the "Total" column, just as exchange rates and percentages are separately configurable.

That would be great!