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 $86.63   10.427%   $95.6629   $95.66   $95.65   $95.70  
  Purchase #2 $90.25   8.335%   $97.7723   $97.77   $97.75   $97.80  
  Purchase #3 $35.60   6.427%   $37.888   $37.89   $37.90   $37.90  
  Purchase #4 $231.26   11.293%   $257.3762   $257.38   $257.40   $257.40  
  Purchase #5 $172.74   3.419%   $178.646   $178.65   $178.65   $178.60  
  Purchase #6 $18.86   3.338%   $19.4895   $19.49   $19.50   $19.50  
  Purchase #7 $173.32   6.235%   $184.1265   $184.13   $184.15   $184.10  
  7 purchase totals = $808.66       $870.9614   $870.97   $871.00   $871.00