Binance offers the ability to convert small amounts of crypto to BNB. You can read more about the process on Binance. Currently, this data is not included when you export your data from Binance, which can lead to some balance discrepancies in your BitcoinTaxes account.
If you have converted dust to BNB on Binance, you'll need to import this data into your BitcoinTaxes Trading Tab. You can do this by manually importing the transactions, or by creating and importing a standard CSV.
You can treat the Dust to BNB conversions as trades. For example, if you've converted .599 TRX to .00253543 BNB, you can add it as a sale of TRX for BNB.