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 $239.59   5.597%   $252.9999   $253.00   $253.00   $253.00  
  Purchase #2 $56.87   13.232%   $64.395   $64.40   $64.40   $64.40  
  Purchase #3 $122.71   11.462%   $136.775   $136.78   $136.80   $136.80  
  Purchase #4 $182.25   9.299%   $199.1974   $199.20   $199.20   $199.20  
  Purchase #5 $208.26   8.843%   $226.6764   $226.68   $226.70   $226.70  
  Purchase #6 $100.38   6.357%   $106.7612   $106.76   $106.75   $106.80  
  Purchase #7 $54.91   8.649%   $59.6592   $59.66   $59.65   $59.70  
  7 purchase totals = $964.97       $1,046.4641   $1,046.48   $1,046.50   $1,046.60