Is it legal for a bar/restaurant to double tax alcohol sales?

We frequent a restaurant that when you have strictly alcohol on your tab there is no tax added in because it is is built into the cost but if we order a single item of food along with alcohol on our tab our entire ending total of the tab is taxed on a whole at 7%. Is this legal? We had a $10.50 total of alcohol and a $2.49 sale of cappuccino. After the cappuccino was added onto the tab, the taxes on this one sale of the cappuccino was $.91. If we would of left the $2.49 sale on this tab along with the alcohol and had added any more sales of alcohol on this tab the taxes would of kept increasing throughout the evening until we tabbed out, therefore double taxing the entire alcohol sales. At the end of the evening if we would of had $40.00 alcohol with the $2.49 cappuccino sales we would of ended up paying $5.46 actually for the cappuccino. Therefore $2.80 extra, instead of $.17 is collected from us the customer in taxes but probably never reported. I believe they are aware of this but have an outdated computer system that does not accommodate this or separate the sales out. Is this legal? We live in Nebraska and this is a gaming institution if that matters at all.