Despite not wanting to be taxed or robbed, I do like this idea. I think 10% is rather high, and instead should be similar to real-life transaction fees, like PayPal's 0.2-2% fee rather than a "tax".
+ Added money sink
+ Players can avoid a transaction fee by transferring cash in-person, leading to more opportunities to rob/get robbed, and in turn create more wanted players for police.
If I'll be honest, I'm not sure how transferring with bank accounts works in MCNR as I have only transferred when next to a player. If bank transfers currently require the sender to be present at an ATM/bank, and this feature is introduced, then you should be able to transfer cash at any location at your convenience.