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 $120.98   4.298%   $126.1797   $126.18   $126.20   $126.20  
  Purchase #2 $206.34   3.570%   $213.7063   $213.71   $213.70   $213.70  
  Purchase #3 $108.35   5.711%   $114.5379   $114.54   $114.55   $114.50  
  Purchase #4 $91.81   10.484%   $101.4354   $101.44   $101.45   $101.40  
  Purchase #5 $216.33   6.609%   $230.6272   $230.63   $230.65   $230.60  
  Purchase #6 $125.51   11.458%   $139.8909   $139.89   $139.90   $139.90  
  Purchase #7 $35.75   4.201%   $37.2519   $37.25   $37.25   $37.30  
  7 purchase totals = $905.07       $963.6293   $963.64   $963.70   $963.60