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 $43.68   8.257%   $47.2867   $47.29   $47.30   $47.30  
  Purchase #2 $118.41   11.671%   $132.2296   $132.23   $132.25   $132.20  
  Purchase #3 $160.37   10.792%   $177.6771   $177.68   $177.70   $177.70  
  Purchase #4 $216.60   5.676%   $228.8942   $228.89   $228.90   $228.90  
  Purchase #5 $237.72   5.443%   $250.6591   $250.66   $250.65   $250.70  
  Purchase #6 $104.72   7.517%   $112.5918   $112.59   $112.60   $112.60  
  Purchase #7 $17.26   7.708%   $18.5904   $18.59   $18.60   $18.60  
  7 purchase totals = $898.76       $967.9289   $967.93   $968.00   $968.00