Since you're only storing data by zip code you're having to dump your data the moment the date and candID change. I'd use a HoHoH myself.

single entries would look something like this:

$hash{$zip}{$ID}{total} for the monetary total regardless of dates.
$hash{$zip}{$ID}{$date} for the monetary total for any individual date.

Unique dates would be stored as keys in the hash, and you could fetch them with keys $hash{$zip}{$ID}.