It depends on your clientele and the pricing of your competition, but you might want to stay with the $1 increments to your top wash, and make it $5, $6, $7, and $8.
I have found that a bump of more than $1 from the "second to the top" and "top" wash can keep some people away. It is more likely for someone who is willing to spend $7, to go up to $8 for the extras you add. $1 extra for the customer to know they are "getting everything" seems to help your top package be one of the better, if not best, sellers - and that should be the goal.
I have seen this hold true even if you have $2 dollar increments on the lower packages, but still make the top bump only $1. For example: $5, $7, $8. Or $5, $7, $9, $10.
Price your top package where you want it, and then set the others so your customers will see the value in purchasing it.