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 $22.75   8.721%   $24.734   $24.73   $24.75   $24.70  
  Purchase #2 $93.38   6.431%   $99.3853   $99.39   $99.40   $99.40  
  Purchase #3 $166.85   5.727%   $176.4055   $176.41   $176.40   $176.40  
  Purchase #4 $157.87   6.578%   $168.2547   $168.25   $168.25   $168.30  
  Purchase #5 $167.60   11.556%   $186.9679   $186.97   $186.95   $187.00  
  Purchase #6 $81.34   13.717%   $92.4974   $92.50   $92.50   $92.50  
  Purchase #7 $26.43   10.646%   $29.2437   $29.24   $29.25   $29.20  
  7 purchase totals = $716.22       $777.4885   $777.49   $777.50   $777.50