First subtract the cost of Mark's groceries from the amount he gives the cashier to find how much he gets in change: $7.00 - $4.20 - $2.05 = $<<7-4.2-2.05=0.75>>0.75
Then subtract the value of a quarter in cents (25) and the value of a dime in cents (10) from the change amount to find how much Mark gets paid in nickels: $0.75 - $0.25 - $0.10 = $<<0.75-0.25-0.10=0.40>>0.40
Now divide the amount Mark gets in nickels by the value per nickel in cents (5) to find how many nickels Mark gets: $0.40 / $0.05/nickel = <<0.40/0.05=8>>8 nickels
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