The coffee industry does have a lot of pay issues, farmers should always be paid higher but I will put that to one side for this conversation.
Roasters are generally underpaid, as someone who has been an underpaid roaster before. They are making minimum wage (or slightly above) for a skilled role and a physically demanding job (70kg coffee sacks are heavy to move around)
But as far as tipping goes that is not something I understand for this, just increase the price by 5% and pay your staff more. People are happy paying more for something knowing that people are paid well.
One company that I really respect as far as pay is Imbibe coffee roasters who give away a good percentage of their profits to their staff and to charity:
https://imbibe.ie/story/