I recall in the UK in 2006, in retail supermarkets, it's been disclosed that the tag price is a cash-only price. That if you pay by a credit card, then the price is 2 or 3% less, but there's an extra 2% or 3% fee for credit card processing.
In the US, sales tax is almost never included in the price tag, so, when you checkout, you get the sales tax itemised separately, including when different jurisdictions charge separate taxes (e.g., county + city sales tax). Hotels in states with a gross-receipts tax often pass this tax back to the consumer as well.
In Eventbrite and many other similar apps, including for donations, the processing fees are nearly always shown separately from the cash price itself; I believe some platforms let the seller decide how it's shown (e.g., "who pays it").