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 $33.72   13.628%   $38.3154   $38.32   $38.30   $38.30  
  Purchase #2 $186.34   5.138%   $195.9141   $195.91   $195.90   $195.90  
  Purchase #3 $68.25   7.401%   $73.3012   $73.30   $73.30   $73.30  
  Purchase #4 $173.93   13.246%   $196.9688   $196.97   $196.95   $197.00  
  Purchase #5 $147.99   4.190%   $154.1908   $154.19   $154.20   $154.20  
  Purchase #6 $132.86   7.397%   $142.6877   $142.69   $142.70   $142.70  
  Purchase #7 $50.97   5.772%   $53.912   $53.91   $53.90   $53.90  
  7 purchase totals = $794.06       $855.2900   $855.29   $855.25   $855.30