I'd do it like this: if it's 25 dirhams, round down; if it's 75 dirhams, round up; if it's 50 dirhams, round it to an even number of riyals (thus sometimes up and sometimes down). Fair enough?
I'd do it like this: if it's 25 dirhams, round down; if it's 75 dirhams, round up; if it's 50 dirhams, round it to an even number of riyals (thus sometimes up and sometimes down). Fair enough?