Congrats on your tip! Always a nice surprise there at the end.
Regarding your question, I’m no 100% sure about this but I believe that the Fiverr doesn’t take a percentage of the tips. So, in case you don’t already know, Fiverr takes 20 percent of each order, meaning 1 dollar for every 5 dollars. Since the order is initially 10 dollars it comes down to 8. As for the tip I believe (again not 100% sure) nothing is deducted from it, meaning you should receive 18 not 16.
My recommendation is to check your earnings tab, and if it’s still confusing I highly recommend getting in touch with the support team at Fiverr, they’ve been extremely helpful but take about 1-2 days to respond
Hope this helps!