The standard currency in the Shire and Bree ( probably based on the monetary system of Arnor) seems to be the silver penny. Below that would be copper coins. Barter would also be common. In the first draft for "The Long-expected Party", Bilbo is said to have spent his last 50 ducats on the party. The One Ring Roleplaying Game adopted a currency based on the old British system:
1 gold piece = 20 silver pennies = 240 copper coins
1 silver penny = 12 copper coins
Tolkien did write about money in Gondor. To quote Tolkien Gateway: "In Gondor, the chief currency was the Castar; a small silver coin known as the Tharni was worth one-fourth of a Castar."I
Information about the castar and tharni didn't come out until way after ICE lost its licence to produce Middle-earth games. Just for fun, here's the system that the game designers came out with. Source: Minas Ithil.
Malanor (orb, sun): 1 mithril piece = 10 gold pieces = 200 silver pieces
Erin (gold crown): 1 gold piece = 20 silver pieces
Nimloth (silver tree): 4 silver pieces = 40 bronze pieces
Celebarn (silver royal): 1 silver piece = 10 bronze pieces = 50 copper pieces
Tamb (bronze penny): 1 bronze piece = 5 copper pieces
Peret (copper half): 0.5 bronze piece = 2.5 copper pieces
Benhar (copper bit): 1 copper piece
Here's a webpage showing the old UK monetary system, photos included.
Yeah, MERP's base monetary system was a decimal one:
1 mithril piece (mp) = 100 gold pieces (gp)
1 gold piece (gp) = 10 silver pieces (sp)
1 silver piece (sp) = 10 bronze pieces (bp)
1 bronze piece (bp) = 10 copper pieces (cp)
1 copper piece (cp) = 10 tin pieces (tp)
Later supplements expanded on this with rates of exchange for Arthedain and Gondor and notes on the coins produced by each kingdom (the default setting for the game was around the year Third Age 1641), which leads to the table that eldariontkd reproduced.
Decipher's The Lord of the Rings Roleplaying Game had it's own monetary system:
LOTR RPG has five coinage Types: copper penny, silver penny, silver piece, gold penny, and gold piece. It uses the classic relation of value mentioned in J.R.R. Tolkien's Books: 1 Goldpiece = 4 Gold Pennies, 1 Goldpenny = 4 Silverpieces, 1 Silverpiece = 4 Silverpennies with the exception of the copperpenny which is = 100 Silverpennies.
Much of the default prices mentioned in the core book is based on research, for example, a Pony in Bree costs exactly four silverpennies- the exact price mentioned in the Book the Lord of the Rings.
Not sure how much of this is canon.
I believe that most of this was developed for the Middle-earth Role Playing (MERP) game, though Gondorian Castar and Tharni, at least, come from Tolkien. In The Lord of the Rings we do see silver pennies being used in Bree.
The Castar, Tharni, and penny were from Tolkien. MERP's Gondorian currency had other names like gold nobles, silver tree, copper bit. To be fair, the game was published way before the Histories were, so a lot of information was not out yet. ICE had to fill in the blanks for the game.