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 $211.76   9.737%   $232.3791   $232.38   $232.40   $232.40  
  Purchase #2 $63.93   6.188%   $67.886   $67.89   $67.90   $67.90  
  Purchase #3 $235.62   3.495%   $243.8549   $243.85   $243.85   $243.90  
  Purchase #4 $34.69   3.242%   $35.8146   $35.81   $35.80   $35.80  
  Purchase #5 $92.50   6.677%   $98.6762   $98.68   $98.70   $98.70  
  Purchase #6 $142.67   10.195%   $157.2152   $157.22   $157.20   $157.20  
  Purchase #7 $115.80   6.759%   $123.6269   $123.63   $123.65   $123.60  
  7 purchase totals = $896.97       $959.4529   $959.46   $959.50   $959.50