Hello Hamid,

I am sharing my thoughts that we applied to achieve this feature. 

We customized the stuff to transfer the daily cash into Bank Account. For that we added a "many2one" field of "account.account" under the "account.journal" which suggests, to which account the amount should be transferred whenever the "Cash box" gets close during end of the day. So here you can specify your Bank Account to which you want to transfer the amount.

Now under the model "account.bank.statement" - POS Register you need to inherit the methods "button_confirm_bank" and "button_confirm_cash". Here you need to post a "account.bank.statement.line" - Statement Line, where you will specify the account, which is been configured under particular register/journal (explained in first para). Also specify the amount with "-ve" sign so that the configured bank account gets debited and your A/R gets credited, so at the end, under your cash box the amount will be set to zero.

 This configuration will give you flexibility and dynamism of transferring the amount automatically and you can easily configure the bank account to which you want to transfer the amount as per the register/journal.

OR

The fastest way is to post a manual jouranl entry where A/R will be credited and your Bank Account will get debited.

Regards