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 $124.85   13.285%   $141.4363   $141.44   $141.45   $141.40  
  Purchase #2 $137.55   8.643%   $149.4384   $149.44   $149.45   $149.40  
  Purchase #3 $160.99   5.451%   $169.7656   $169.77   $169.75   $169.80  
  Purchase #4 $56.92   10.495%   $62.8938   $62.89   $62.90   $62.90  
  Purchase #5 $26.83   6.338%   $28.5305   $28.53   $28.55   $28.50  
  Purchase #6 $240.63   10.655%   $266.2691   $266.27   $266.25   $266.30  
  Purchase #7 $118.32   3.724%   $122.7262   $122.73   $122.75   $122.70  
  7 purchase totals = $866.09       $941.0599   $941.07   $941.10   $941.00