I voted All or Almost All based on where I grew up, but It Depends based on where we live now.
First off, where we live now...we've been out since late May. DD17 graduated on May 25th. Their district allows kids to exempt finals in a number of situations, so it's also not uncommon for underclassmen to be out a lot as well towards the end. Underclassmen had finals the week after graduation, but DD15 exempted a bunch or took some in class the week before, so I think she had two on Monday, May 27th and was done.
Where I grew up, they are still in school this week. I don't know if it's like it was when I was there, but nobody missed the end of school. Finals went up until the day before the last day and there were zero exemptions. I looked at their calendar last night and it looked similar to the structure over 30 years ago. Senior prom, I think, was on Friday...which is wild to me since DD17 had hers on April 20th. In any event, today is likely senior skip day, but it was always normal to attend last day of school. They used to require it for you to be consider complete and release grades, GPAs, rankings, etc.