Использование SBJson :
NSString *json = @"{lhs: "2 U.S. dollars",rhs: "89.7988506 Indian rupees",error: "",icc: true}"
NSDictionary *jsonDict = [json JSONValue];
NSString *lhs = [jsonDict objectForKey:@"lhs"];
NSString *rhs = [jsonDict objectForKey:@"rhs"];
...