Weight not always adding up correctly

[idlerob]

Im getting this right problem with my table rate its used in a contribution which is just a modified version of the zones one but allows me to have another one for recorded delivery. All my products at the moment have weight of 0.1 eg 100g most the time the shipping gets added up correctly but for three products which should be 0.3 seems to always add up wrong and be set the the next cost up for 4 products. here is my table. Id be so happy if someone could help out its driving me mad.

 

.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

 

cheers