Yes I know this is after your evening, but a few ideas for the future.
1) You need to spot check your competition for things like this and present it as market research. It will impress them that you have done your homework.
2) A moderate/reasonable price gives them room to feel good about being more generous by rounding up or otherwise tipping.
3) BE SMART. Do not go against their rules, bc you work for them, you speak for them and are their eyes and ears. If you can be pleasant but firm in keeping their absolute MUSTs/MUST NOTs intact...then you will earn respect and trust and repeat bus. and references. 😊