How to disable default entry of old/previous customer on POS screen?

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Looking for some help.  We just began using the POS, but running into a 
lot of users errors especially when it comes to the Customer field.  The 
default behavior is for the Customer field to default to the old customer 
(or the Customer from the previous sale). Our users though forget to 
change this field when the next sale is entered for a different customer, 
therefore, the sale gets posted under the previous customer's name which 
is incorrect.  How can I change this so the Customer field does not 
default to the previous customer and instead begins with no customer 
selection?  This would then force the salesperson to enter a customer in 
the Customer field.  Ideally, when the salesperson first select POS>Sale, 
the pos screen would open with no entry in the Customer field, but the 
cursor placed in that field waiting for entry from the salesperson.

Best Regards,
Steven Marshall

Taty Lee Boutique
11705 Jones Bridge Rd., B206
Alpharetta, GA 30005
770-410-6964

"Once you experience the stylish comfort of Brazilian-cut jeans, you will 
demand nothing less!"