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 $175.89   11.396%   $195.9344   $195.93   $195.95   $195.90  
  Purchase #2 $198.69   10.140%   $218.8372   $218.84   $218.85   $218.80  
  Purchase #3 $52.49   5.719%   $55.4919   $55.49   $55.50   $55.50  
  Purchase #4 $158.53   5.554%   $167.3348   $167.33   $167.35   $167.30  
  Purchase #5 $177.35   11.353%   $197.4845   $197.48   $197.50   $197.50  
  Purchase #6 $76.88   3.489%   $79.5623   $79.56   $79.55   $79.60  
  Purchase #7 $66.48   10.260%   $73.3008   $73.30   $73.30   $73.30  
  7 purchase totals = $906.31       $987.9459   $987.93   $988.00   $987.90