There is no real confirmation of what tipping does to your gaming experience, however some people are saying it may increase your shiny chance!
This is still speculation, however this theory is well supported - it definitely makes sense since maybe the shiny chance could be increased due to people tipping everyone. And I can personally support this as I never tip people and I haven't found a single shiny as of yet. 3:
But apart from this wonderful theory, there is no confirmed usage in tipping people, so unless your obsessed with shinies don't tip people. xD
Hope I helped. :)