95% is not a good idea for traffic of a bursty nature, however, for traffic that is consistently on the bell curve.. it works rather well.
An example of that type of traffic is below.
Although this port bursted up to 30+Mbits on a few occasions. the 95% on this would be billed 25.501 Mbits.
Some providers bill on the average, at the 95th, at the 100%, Average in + Average Out. Max in + Max Out. It just depends on your type of traffic.
Some say 95th is bad. I have several customers pushing over 30 Mbits per server port and they are comfortable with this arrangement. It?s fair to the SP and the customer.