Green’s Dictionary of Slang

(Aus.) a bar game in which the winner buys drinks for the players; usu. in Tambaroora muster, a group of drinkers pooling their money and buying one ‘wholesale’ round, since in this way more alcohol can be purchased.

1882		A.J. Boyd Old Colonials 7: The proliferation of the grog shanty and the vogue of the ‘Tambaroora muster.’.
1895		C. Crowe Aus. Sl. Dict. 84: Tambaroora, a game of a shilling each in the hat and the winner shouts.
1897		Bulletin (Sydney) 18 Dec. n.p.: (Red Page) The essence of a present-day tambaroora is a sweep for the purchase of drinks — frequently on the principle that more liquor can be purchased wholesale for 1s. 6d. than six thirsty people can buy for 3d. each. Hence ‘tambaroora muster’, when the droughty party musters all the coin it’s possessed of, and one individual goes and bargains for the beer.
1900–10		Stephens & O’Brien Materials for a Dict. of Aus. Sl. [unpub. ms.] 155: TAMBAROORA, OR TAMBAROORA MUSTER: a mustering up of money for shouting purposes.
1945		Baker Aus. Lang. 172: Just as the shout is an institution in this part of the world so are the [...] Kentucky,Tambaroora muster and a few other variations on the theme, all of which concern the creation of a jack-pot, usually with the object of buying drinks. The Tambaroora — taken from the name of an eastern township — dates from the early 1880s. The idea behind these expressions [...] is that everyone pays for himself.
1959		Baker Drum.