Response:
1) Total expenditure of the customer is $1300
2) Overall amount totals $1345.50
Step-by-step calculation:
Given:
1) Customer: “I wish to buy 20 products at $65.00 each.
2) Employee: “There is a 3.5% sales tax in your state.”
To determine: 1) What is my grand total?
2) Your total amount is?
Calculation:
1) The cost for one product is $65
Cost for 20 products is 
Thus, the total spending is $1300
2) The sales tax rate = 3.5%
Therefore, the sales tax on the customer's purchase equals

Total = $1300 + $45.50 = $1345.50
Conclusively, the total is $1345.50