If you withdraw the money from the ATM, you can only get money 100,or 200,or more, but you can not get 150,or 152, or 278. It means that you can only get money out with the unit of hundred.
If you open your account in Bank of China in Zhongshan, you can only be free to withdraw money from different banks of B/C in Zhongshan. If you withdraw money from other banks in Zhongshan, you will be charged. If you withdraw from other B/C from another city, you will also be charged. They will charge you according to the amount you will withdraw. The minimum charge is 2 RMB. It seems like to charge 1RMB for 100RMB that you have withdrawn. You will also be charged 10 RMB every year as the fee for the bank mamagement