Its not actually necessary but rather it would really be just depending on someone whether he would be giving out some tips on the time he would win jackpot or something big.
I dont know but it is really becoming a common gesture which does show up some appreciation and thinking that its just better to give a small amount at least into that
attendant or someone whose on the table or something.You would really be baring in your mind that he/she might be part of you on being lucky.
So its a personal choice whether you would be tipping out or not, its your choice on which one you would really be doing so.