You can offer a deal like buy 3 or more tickets get 10% off and buy 4 or more get 15% off. This is set at the event level. So different events can have different discounts.
Flat Rate Discount
You can also offer flat rate discounts, like buy 2 tickets get $20 off. If you set the discount to the same value as a ticket price you can run a deal like buy 2 get 1 free.