FOB pricing.. I need to multiply by 4 decimal places

Hello! I am trying to update the pricing on an invoice, to show FOB pricing.  The invoice is in USD.  I can enter the price (USD) as 4 decimal places, but I cannot multiply it by 4 decimal places.

If I have 50 different items on an invoice, I don't want to calculate the FOB cost for each item separately.  I want to multiply the price (USD) by an adjusting percentage. That sounds really confusing, but it isn't!

Example:

6 units @ 688.10 usd = 4128.60 usd.

To add freight costs : x 1.06934 - calculated separately.

If I multiply 688.10 by 1.06934 outside of MYOB, I get 735.8097 each, 4,414.86 for 6 units.

If I multiply the unit cost 688.10 in MYOB, I can only multiply by 1.06, I get 729.39, 4,376.32 for 6 units.  Too inaccurate to use, out by $38.54.. and that's just the first line.

Does anyone know how I can multiply each line by 4 decimal places?  I just want to click on the unit price (usd) and *1.06934.

Any help will be appreciated :-) 

Vanessa