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 $32.98   6.256%   $35.0432   $35.04   $35.05   $35.00  
  Purchase #2 $78.27   13.366%   $88.7316   $88.73   $88.75   $88.70  
  Purchase #3 $25.69   5.678%   $27.1487   $27.15   $27.15   $27.10  
  Purchase #4 $180.36   11.273%   $200.692   $200.69   $200.70   $200.70  
  Purchase #5 $177.68   10.824%   $196.9121   $196.91   $196.90   $196.90  
  Purchase #6 $186.96   5.593%   $197.4167   $197.42   $197.40   $197.40  
  Purchase #7 $176.49   7.740%   $190.1503   $190.15   $190.15   $190.20  
  7 purchase totals = $858.43       $936.0946   $936.09   $936.10   $936.00