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 $185.36   9.196%   $202.4057   $202.41   $202.40   $202.40  
  Purchase #2 $55.29   7.351%   $59.3544   $59.35   $59.35   $59.40  
  Purchase #3 $25.30   6.683%   $26.9908   $26.99   $27.00   $27.00  
  Purchase #4 $186.49   12.109%   $209.0721   $209.07   $209.05   $209.10  
  Purchase #5 $96.32   8.406%   $104.4167   $104.42   $104.40   $104.40  
  Purchase #6 $164.44   13.733%   $187.0225   $187.02   $187.00   $187.00  
  Purchase #7 $187.77   4.604%   $196.4149   $196.41   $196.40   $196.40  
  7 purchase totals = $900.97       $985.6771   $985.67   $985.60   $985.70