In the USA tipping is 15% or 20% or more of the bill not including tax. A pet peeve of mine is restaurants that try to have customers leave a 20% tip including tax.
"Subtotal" is less specific. If there was a bar visit required, you'll have two subtotals but one net (both activities added together). So, I am guessing this is either a fine dining visit or the person who wrote it is used to writing for those.