Defining Rate for SMS

Hello Anton and thank you for great work !
I have managed to install and activate PlaySMS and Kannel, but have one question.
When defining rate for prefix only 3 digits after decimal dot is accepted while most of carriers are billing using 4 or 5 digits after the dot.
Is there a way to configure it (may be somewhere in the code ) ?

Thank you very much in advance !

Regards,
Vasil