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 $59.99   4.280%   $62.5576   $62.56   $62.55   $62.60  
  Purchase #2 $168.87   10.451%   $186.5186   $186.52   $186.50   $186.50  
  Purchase #3 $43.52   10.262%   $47.986   $47.99   $48.00   $48.00  
  Purchase #4 $228.46   4.485%   $238.7064   $238.71   $238.70   $238.70  
  Purchase #5 $235.69   6.302%   $250.5432   $250.54   $250.55   $250.50  
  Purchase #6 $78.36   7.109%   $83.9306   $83.93   $83.95   $83.90  
  Purchase #7 $121.91   6.148%   $129.405   $129.41   $129.40   $129.40  
  7 purchase totals = $936.80       $999.6474   $999.66   $999.65   $999.60