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 $209.40   8.274%   $226.7258   $226.73   $226.75   $226.70  
  Purchase #2 $228.59   12.587%   $257.3626   $257.36   $257.35   $257.40  
  Purchase #3 $41.53   12.343%   $46.656   $46.66   $46.65   $46.70  
  Purchase #4 $123.81   8.738%   $134.6285   $134.63   $134.65   $134.60  
  Purchase #5 $195.61   7.552%   $210.3825   $210.38   $210.40   $210.40  
  Purchase #6 $34.58   12.128%   $38.7739   $38.77   $38.75   $38.80  
  Purchase #7 $46.73   3.395%   $48.3165   $48.32   $48.30   $48.30  
  7 purchase totals = $880.25       $962.8458   $962.85   $962.85   $962.90