To go halves is to split the cost equally between two. Go halves on a taxi.
It is only ever between two, since three people would go thirds and nobody says that. To go halves is settled before the bill rather than after, which avoids the awkwardness.
1phrasego halvesTo split the cost equally between two.
“They would go halves on everything and keep no accounts at all.”
go halves is a phrase.
Practised in Idioms