On my clerics at all levels I accept all donations with thanks. I also tend to vastly increase my willingness to use my own resources (even beyond whatever is donated) if I know that a party is being generous with me.

I will sometimes ask if the clerics needs anything and then support them if they say yes. Long time players often say they are fine. If I'm asked in that way I do tend to say that I'm fine, but I also do up willingness for my own resource use.

Tipping at the end of a tough quest is nice, but it doesn't help the party out as much.