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 $216.73   11.232%   $241.0731   $241.07   $241.05   $241.10  
  Purchase #2 $126.40   8.177%   $136.7357   $136.74   $136.75   $136.70  
  Purchase #3 $19.42   6.578%   $20.6974   $20.70   $20.70   $20.70  
  Purchase #4 $70.32   9.320%   $76.8738   $76.87   $76.85   $76.90  
  Purchase #5 $121.76   12.448%   $136.9167   $136.92   $136.90   $136.90  
  Purchase #6 $200.89   11.770%   $224.5348   $224.53   $224.55   $224.50  
  Purchase #7 $206.26   10.363%   $227.6347   $227.63   $227.65   $227.60  
  7 purchase totals = $961.78       $1,064.4662   $1,064.46   $1,064.45   $1,064.40