Guatemala has an international departure tax of $30—check your air ticket carefully as it's sometimes included in the price—and a domestic departure tax of Q5. You also have to pay a Q20 airport security fee.
Most Guatemalan hotels and some tourist restaurants charge an additional 10% tourist tax. There is a 10% V.A.T. on most consumer products, but it is already included in the display price. There is no tax refund scheme for visitors.