The standard amount for chargeback fees in the industry varies but in most cases it is a standalone fee of $10-$30 per chargeback or it is embedded into alternate fees such as credit card fees, licensing fees or other financial activity.
So, in short: you were charged a chargeback fee previously, you just didn't see it as a separate charge.
At Toast, the fee is transparent and is currently $15, intended to cover the cost of transmission of chargeback data, costs associated with the chargeback itself and coverage against the chargeback exposure against Toast for credit card processing.
The fee is not waived, unless it was a result of a known Toast processing outage or issue. Chargeback details are disclosed as part of the Toast Merchant agreement (http://pos.toasttab.com/merchant-agreement - Section 7.8 - 7.11).