Square POS bar

Good question. Small but very important detail. Unfortunately Square Register doesn't appear to have a "save for later" option for the orders (I'm using the newest version as of this posting).
You might want to look at some other options, like POS Lavuor InStore to help with your bar. Vend, and Lightspeed Cloud are some other more feature rich POS to look at too. There's also ShopKeep, but for me and a few of my friends ShopKeep has been a very frustrating experience.

The second part of your question is a bit tricky. The Square rate is a middle of the road rate. With a regular merchant account the guy or girl that sold it to you probably advertised a swipe rate of 1.6%. Keyword being swipe. That rate sounds a lot better than Squares BUT hidden in the fine print is that there are a ton of different price tiers rates based on the type of card.

For example, most likely you have a credit card that you earn points or milage with and maybe a debit card for your checking account. A majority of people will use their points card to purchase items so they can get "free" money back.

Well, those points cards charge the merchant a different rate. Not the 1.6% rate that is advertised but an ugly rate of 3+%. Also Amex and Discover are in the 3+ range.

There used to be a great resource site called FeeFighters that had some cool credit card calculators on it, but looks like they've been bought by Groupon :(

So the 2.75% isn't a "bad" rate if you look at the average rate you would be paying using a normal merchant account. It's also nice to know exactly what your swipe fee is at the time of payment, not a month later in some super cryptic merchant bill.