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 $223.73   10.169%   $246.4811   $246.48   $246.50   $246.50  
  Purchase #2 $62.98   4.785%   $65.9936   $65.99   $66.00   $66.00  
  Purchase #3 $236.86   4.531%   $247.5921   $247.59   $247.60   $247.60  
  Purchase #4 $84.42   10.484%   $93.2706   $93.27   $93.25   $93.30  
  Purchase #5 $150.90   4.595%   $157.8339   $157.83   $157.85   $157.80  
  Purchase #6 $79.87   4.321%   $83.3212   $83.32   $83.30   $83.30  
  Purchase #7 $23.77   3.723%   $24.655   $24.66   $24.65   $24.70  
  7 purchase totals = $862.53       $919.1475   $919.14   $919.15   $919.20