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 $112.84   5.246%   $118.7596   $118.76   $118.75   $118.80  
  Purchase #2 $146.34   8.601%   $158.9267   $158.93   $158.95   $158.90  
  Purchase #3 $46.92   7.535%   $50.4554   $50.46   $50.45   $50.50  
  Purchase #4 $37.97   11.836%   $42.4641   $42.46   $42.45   $42.50  
  Purchase #5 $208.47   3.395%   $215.5476   $215.55   $215.55   $215.50  
  Purchase #6 $125.51   10.286%   $138.42   $138.42   $138.40   $138.40  
  Purchase #7 $250.63   9.289%   $273.911   $273.91   $273.90   $273.90  
  7 purchase totals = $928.68       $998.4844   $998.49   $998.45   $998.50