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 $82.83   11.851%   $92.6462   $92.65   $92.65   $92.60  
  Purchase #2 $94.34   3.680%   $97.8117   $97.81   $97.80   $97.80  
  Purchase #3 $30.58   13.133%   $34.5961   $34.60   $34.60   $34.60  
  Purchase #4 $233.25   11.810%   $260.7968   $260.80   $260.80   $260.80  
  Purchase #5 $72.57   3.162%   $74.8647   $74.86   $74.85   $74.90  
  Purchase #6 $197.75   13.716%   $224.8734   $224.87   $224.85   $224.90  
  Purchase #7 $21.89   11.271%   $24.3572   $24.36   $24.35   $24.40  
  7 purchase totals = $733.21       $809.9461   $809.95   $809.90   $810.00