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 $61.64   5.308%   $64.9119   $64.91   $64.90   $64.90  
  Purchase #2 $227.71   3.791%   $236.3425   $236.34   $236.35   $236.30  
  Purchase #3 $119.64   3.856%   $124.2533   $124.25   $124.25   $124.30  
  Purchase #4 $177.43   10.333%   $195.7638   $195.76   $195.75   $195.80  
  Purchase #5 $29.45   4.393%   $30.7437   $30.74   $30.75   $30.70  
  Purchase #6 $46.72   4.175%   $48.6706   $48.67   $48.65   $48.70  
  Purchase #7 $194.25   6.493%   $206.8627   $206.86   $206.85   $206.90  
  7 purchase totals = $856.84       $907.5485   $907.53   $907.50   $907.60