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 $67.57   8.167%   $73.0884   $73.09   $73.10   $73.10  
  Purchase #2 $117.87   3.158%   $121.5923   $121.59   $121.60   $121.60  
  Purchase #3 $153.53   3.208%   $158.4552   $158.46   $158.45   $158.50  
  Purchase #4 $179.82   3.432%   $185.9914   $185.99   $186.00   $186.00  
  Purchase #5 $10.41   6.119%   $11.047   $11.05   $11.05   $11.00  
  Purchase #6 $138.30   9.380%   $151.2725   $151.27   $151.25   $151.30  
  Purchase #7 $148.82   9.649%   $163.1796   $163.18   $163.20   $163.20  
  7 purchase totals = $816.32       $864.6264   $864.63   $864.65   $864.70