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 $239.29   8.759%   $260.2494   $260.25   $260.25   $260.20  
  Purchase #2 $104.96   8.359%   $113.7336   $113.73   $113.75   $113.70  
  Purchase #3 $117.87   8.548%   $127.9455   $127.95   $127.95   $127.90  
  Purchase #4 $242.76   3.639%   $251.594   $251.59   $251.60   $251.60  
  Purchase #5 $80.52   5.439%   $84.8995   $84.90   $84.90   $84.90  
  Purchase #6 $225.89   13.610%   $256.6336   $256.63   $256.65   $256.60  
  Purchase #7 $238.63   9.558%   $261.4383   $261.44   $261.45   $261.40  
  7 purchase totals = $1,249.92       $1,356.4939   $1,356.49   $1,356.55   $1,356.30