Audit procedures for tellers using TCRs

Employee at a credit_union ($383MUSA)
We have recently gone from TCDs to TCRs. We have the cash counts down, we have the forms to input all the cash information.  What we are looking for are internal controls to put in place for tellers.   Not that we have had a problem but an incident has happened for us to evaluate our audit process.   During busy times when a very large cash deposit is made the teller delays the deposit of cash to the machine.  The cash is set aside until they have time to put the cash in the recycler which is a great concern thus delaying a deposit.   If a teller took a deposit for $100 and gave the customer a receipt for $100 but only put in $75 in the machine what audit procedures would be in place?  I know the machine would be out of balance but are there reports that substantiate the receipt versus the deposit.  And, how would we know if there is a fictitious transaction?