add decimal point in product quantity

i am using open-cart 1.5.5.1 with fresh market theme.i want to use decimal points in product quantity.
i have already tried this code
http://forum.opencart.com/viewtopic.php?t=20441
it works fine for default theme but when i use fresh market theme it will not count decimal in quantity.when i order for 1.5 quantity then it count 2 product and when i order 1.4 it count as 1 product in my cart.
please help where i'm doing mistake?