It is up to the law firm to understand the law surrounding surcharges in their state. Due to frequent changes and variance from state to state, MONESQ does not support this directly.
If you need to add a line item to an invoice in MONESQ Plus, you could add a flat fee line item to itemize the surcharge. The law firm can add surcharges if they choose in this manner. However, MONESQ cannot recommend this as it is generally frowned upon.
Please consult with your state bar requirements.