The holidays are a time when the act of giving comes with joy as well as complications. Many of us buy gifts for people we know. We enjoy seeing a friend or family member open a present we selected. It's satisfying to send off a special fruit cake to someone deserving in another time zone.  Giving gratuities is more complicated. It has become popular to give a little something to people in service industries, people we rely on. From postal carriers to personal trainers, the list can be long. The basic questions are: Who do I tip and how much do I give? It's a matter of opinion among most …