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 $61.87   4.788%   $64.8323   $64.83   $64.85   $64.80  
  Purchase #2 $186.75   5.676%   $197.3499   $197.35   $197.35   $197.30  
  Purchase #3 $197.66   13.514%   $224.3718   $224.37   $224.35   $224.40  
  Purchase #4 $60.38   4.546%   $63.1249   $63.12   $63.10   $63.10  
  Purchase #5 $126.42   10.301%   $139.4425   $139.44   $139.45   $139.40  
  Purchase #6 $243.89   3.846%   $253.27   $253.27   $253.25   $253.30  
  Purchase #7 $42.47   13.689%   $48.2837   $48.28   $48.30   $48.30  
  7 purchase totals = $919.44       $990.6751   $990.66   $990.65   $990.60