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 $67.52   9.198%   $73.7305   $73.73   $73.75   $73.70  
  Purchase #2 $240.42   13.218%   $272.1987   $272.20   $272.20   $272.20  
  Purchase #3 $46.63   9.159%   $50.9008   $50.90   $50.90   $50.90  
  Purchase #4 $130.89   4.182%   $136.3638   $136.36   $136.35   $136.40  
  Purchase #5 $70.50   8.288%   $76.343   $76.34   $76.35   $76.30  
  Purchase #6 $153.61   5.609%   $162.226   $162.23   $162.25   $162.20  
  Purchase #7 $44.83   13.622%   $50.9367   $50.94   $50.95   $50.90  
  7 purchase totals = $754.40       $822.6995   $822.70   $822.75   $822.60