They recently started having P20 coins (worth about .40) but everything above that is paper. The highest denomination they have here is a 1000-peso bill (worth about $20). It would be a real pain when you get large amounts of money if they were coins instead.
The denominations here are 1,5,10,20,50,100,500 and 1000. Maybe up to a P50 coin would be okay. After that it would start getting too heavy in your pocket.
Things here in The Philippines are a whole lot cheaper than in Japan. So, you don't really need to carry so much cash (and almost everything is cash only).
I was stationed in Okinawa (Kadena) twice (my 2 favorite assignments).
I never heard of a $5 coin before. Not a current one anyway.