[gamblor956]

Depends on the ERP. Some store a running balance in the account ledger; others sum and cache the results until the data changes; and the some actually sum everything every time because accuracy matters more than speed.

Generally, the most practical way to do is to "finalize" a number periodically (monthly and annually) when the books for the prior period have been "closed" (locked from further edits) and then sum only transactions taking place since the last closed balance. Most major ERPs do this.