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 $59.53   8.564%   $64.6281   $64.63   $64.65   $64.60  
  Purchase #2 $90.30   9.660%   $99.023   $99.02   $99.00   $99.00  
  Purchase #3 $230.26   13.744%   $261.9069   $261.91   $261.90   $261.90  
  Purchase #4 $85.63   7.545%   $92.0908   $92.09   $92.10   $92.10  
  Purchase #5 $109.96   8.515%   $119.3231   $119.32   $119.30   $119.30  
  Purchase #6 $48.64   5.491%   $51.3108   $51.31   $51.30   $51.30  
  Purchase #7 $239.43   9.392%   $261.9173   $261.92   $261.90   $261.90  
  7 purchase totals = $863.75       $950.2000   $950.20   $950.15   $950.10