So stuck with this shipping probelm

[idlerob]

I use table rates for my shipping with different zones and below is my table weights for one of my zones. All my products at the moment are set to 0.1. When i go to checkout it seems all amounts of products work except for when i have 3 products = total weight being 0.3. My postage cost should be ?2 but always comes out as ?2.50.

 

.10:1.00,.20:1.50,.30:2.00,.40:2.50,.50:3.00,.60:3.50,.70:4.00,.80:4.50,.90:5.00

,1.00:5.50,1.10:6.00,1.20:6.50,1.30:7.00,1.40:7.50,1.50:8.00,1.60:8.50,1.70:9.00,

1.80:9.50,1.90:10.00,2.00:10.50

 

If i have 4 products the shipping stays right at ?2.50 but just for three products it wont set the right cost????

 

please help its killing me!!

 

 

thanks