CDR to MySQL with billsec in minutes (not seconds)

I have CDR in MySQL databases for counting billsec. Then with commands MYSQL(Connect… ), MYSQL(Query… ), … , Asterisk retrieve sum in (seconds) for each client and compares them with the specified limit before invoke command Dial() for outgoing calls.

All works fine, but still one problem.

My small billing works with per-second, but I need per-minutes billing. E.g. client with number 7777 call to the outside number 0935555555 with call duration 50 sec, but in the database should be 1, if duration 1 minute and 30 sec - ${CDR(billsec)} must be 2 and so on.

Those who are thinking about it?