Discount percentage calculates wrong 1.3.9b

[waddtown]

I have set up a discount code for 10% off minimum order £25.53 (not including shipping), however the discount is always 4p out see attached picture
if I have a product @£31.00 it calculates the discount as £3.06 whereas it should be £3.10
I have include tax set to false recalculate tax to standard
It doesn't matter what combination of products I add its always 4p out
website url www.ukchildrensjewellery.co.uk

[waddtown]

Any ideas anyone? really need to get this sorted