Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $184.63   10.166%   $203.3995   $203.40   $203.40   $203.40  
  Purchase #2 $96.48   13.871%   $109.8627   $109.86   $109.85   $109.90  
  Purchase #3 $196.89   10.354%   $217.276   $217.28   $217.30   $217.30  
  Purchase #4 $58.99   7.594%   $63.4697   $63.47   $63.45   $63.50  
  Purchase #5 $177.71   7.235%   $190.5673   $190.57   $190.55   $190.60  
  Purchase #6 $55.57   8.701%   $60.4051   $60.41   $60.40   $60.40  
  Purchase #7 $237.65   10.517%   $262.6437   $262.64   $262.65   $262.60  
  7 purchase totals = $1,007.92       $1,107.6240   $1,107.63   $1,107.60   $1,107.70