WP Crowdfunding Pledge ammount only whole numbers

Hi there, I would like to change my reward amount to €5,5 euro instead of €5
Currently I have a site where one can donate sunflowers. Each meter of sunflowers costs €1,10 meter. I have rewards for 5 meters, 10, 25, 50, 100 and 500 meters.
problem is when someone wants to fund 5 meters this should cost €5,5 but unfortunate I am not alowed to use broken numbers (5,50 euro) Is this possible to change.

The page I need help with: [log in to see the link]