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 $64.89   12.758%   $73.1687   $73.17   $73.15   $73.20  
  Purchase #2 $92.69   13.529%   $105.23   $105.23   $105.25   $105.20  
  Purchase #3 $235.83   4.295%   $245.9589   $245.96   $245.95   $246.00  
  Purchase #4 $38.71   5.181%   $40.7156   $40.72   $40.70   $40.70  
  Purchase #5 $164.71   13.502%   $186.9491   $186.95   $186.95   $186.90  
  Purchase #6 $35.49   3.578%   $36.7598   $36.76   $36.75   $36.80  
  Purchase #7 $250.64   8.759%   $272.5936   $272.59   $272.60   $272.60  
  7 purchase totals = $882.96       $961.3757   $961.38   $961.35   $961.40