Why does the broker need exchange files like trades, positions, STT, stamp duty, and other charges every day? The exchange has already published all charges. As per Zerodha’s list of all charges: List of all fees, charges, and taxes on trading and investing – Zerodha
The trade/position files published by the Stock exchange are considered the absolute source of truth by any broker and thus are critical for carrying out the trade process and the billing activities. It’s hard to rely on any other source to obtain this info, even though brokers have this data available in their trading systems etc. Even broker OMS/RMS vendors have built their systems to accept upload of position files in the Exchange format itself.
The rate of STT varies for every scrip, further it varies if the trade is intraday/delivery. Brokers may choose to do these calculations themselves or simply use the exchange file since it’s readily made available by the exchange. Even though this adds a layer of dependency, you’re assured of the values not being calculated incorrect 
Sames goes with Stamp duty.
So yes, while one can build systems to calculate STT, Stamp duty, brokers find reassurance in utilizing the stock exchange trade and position files to manage their day-to-day billing processes.
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