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 $21.32   11.747%   $23.8245   $23.82   $23.80   $23.80  
  Purchase #2 $145.48   5.762%   $153.8626   $153.86   $153.85   $153.90  
  Purchase #3 $84.68   8.568%   $91.9354   $91.94   $91.95   $91.90  
  Purchase #4 $125.88   5.590%   $132.9167   $132.92   $132.90   $132.90  
  Purchase #5 $168.57   10.315%   $185.958   $185.96   $185.95   $186.00  
  Purchase #6 $136.25   12.181%   $152.8466   $152.85   $152.85   $152.80  
  Purchase #7 $51.49   11.874%   $57.6039   $57.60   $57.60   $57.60  
  7 purchase totals = $733.67       $798.9477   $798.95   $798.90   $798.90