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 $85.99   12.434%   $96.682   $96.68   $96.70   $96.70  
  Purchase #2 $35.27   7.584%   $37.9449   $37.94   $37.95   $37.90  
  Purchase #3 $26.95   4.456%   $28.1509   $28.15   $28.15   $28.20  
  Purchase #4 $169.30   12.479%   $190.4269   $190.43   $190.45   $190.40  
  Purchase #5 $223.44   11.639%   $249.4462   $249.45   $249.45   $249.40  
  Purchase #6 $164.93   8.344%   $178.6918   $178.69   $178.70   $178.70  
  Purchase #7 $76.36   10.646%   $84.4893   $84.49   $84.50   $84.50  
  7 purchase totals = $782.24       $865.8320   $865.83   $865.90   $865.80