Hullo Karen!
Taxes should be included, so no worries there.
As for gratuity, or tipping, if your party is 6 or more people an 18% gratuity is automatically added by Disney.
If your group is under 6 people it is customary in the US to tip between 15% to 20% of your total bill (the total before taxes, if any, are added).
I noticed the last time I dined in Disney that my ticket actually had a tipping guide at the bottom with the suggested amount to leave based on my ticket. I didn't have to do any of the math...which always makes me happy! I don't know if they do this at every eatery in Disney, but please peek to see if it's there for you.
I hope you have a great holiday in Disney World! August is almost here!