This means that the rider was charged $8.60 and he chose 10% option, if such available. If % not available on Juno, only numbers, then the rider is a complete moron having to waste his time to type up these random numbers.
50 cent that's outright classic. If someone gave me 50 cent or 1 dollar I would hand it back to him and say you must need this much more than I do and then drop the mic! These apps have created a disgusting culture of self entitled, selfish ingrates.