what I should use if I want to round up, meaning that if someone has parked from 3:30 till 4:15 it registers 2 half an hours, but 1 half till 4:14

Question

I tried with divmode but couldnt succeed. I need to make the code give me 2 half an hours in case I parked from 3:30 till 4:15 but 1 half an hour from 3:30 till 4:14 (just a