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 $23.99   8.743%   $26.0874   $26.09   $26.10   $26.10  
  Purchase #2 $149.25   5.639%   $157.6662   $157.67   $157.65   $157.70  
  Purchase #3 $16.59   10.108%   $18.2669   $18.27   $18.25   $18.30  
  Purchase #4 $117.85   7.648%   $126.8632   $126.86   $126.85   $126.90  
  Purchase #5 $114.44   9.602%   $125.4285   $125.43   $125.45   $125.40  
  Purchase #6 $175.83   13.537%   $199.6321   $199.63   $199.65   $199.60  
  Purchase #7 $150.25   6.147%   $159.4859   $159.49   $159.50   $159.50  
  7 purchase totals = $748.20       $813.4302   $813.44   $813.45   $813.50