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 $66.45   8.617%   $72.176   $72.18   $72.20   $72.20  
  Purchase #2 $73.91   10.250%   $81.4858   $81.49   $81.50   $81.50  
  Purchase #3 $146.30   8.679%   $158.9974   $159.00   $159.00   $159.00  
  Purchase #4 $234.63   11.302%   $261.1479   $261.15   $261.15   $261.10  
  Purchase #5 $197.73   8.848%   $215.2252   $215.23   $215.25   $215.20  
  Purchase #6 $22.95   6.553%   $24.4539   $24.45   $24.45   $24.50  
  Purchase #7 $50.61   6.219%   $53.7574   $53.76   $53.75   $53.80  
  7 purchase totals = $792.58       $867.2436   $867.26   $867.30   $867.30