One thing to keep in mind :
Tipping is about the location you are visiting, NOT the location you are coming from.
If tipping is not customary in your home town, state, province, country... that has zero to do with going to another country, state, province, town and tipping is customary. If it's customary and you are there and you are using the services you tip whether you would back home or not. Where you are visiting its the norm of that local situation.
If you go to France and eat diner and the custom is to round up the bill a Euro or two than do so if the situation warrants it, don't leave a $20 euro tip. If you come to America and you eat dinner and the custom is 20% and the situation warrants it then you leave $40.00 on a two hundred dollar tab. Same for diving, no different. If you go to Fiji and the local custom is do not tip the dive master you don't tip him. If you go the the Florida keys and the custom is to tip a communal tip jar do so. If you go to Mexico and the custom is to tip the dive master and the captain, do so. It doesn't make any difference what your local custom is, you aren't home.