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 $171.94   13.853%   $195.7588   $195.76   $195.75   $195.80  
  Purchase #2 $177.97   5.524%   $187.8011   $187.80   $187.80   $187.80  
  Purchase #3 $234.67   11.383%   $261.3825   $261.38   $261.40   $261.40  
  Purchase #4 $70.96   4.156%   $73.9091   $73.91   $73.90   $73.90  
  Purchase #5 $206.79   4.723%   $216.5567   $216.56   $216.55   $216.60  
  Purchase #6 $216.86   13.593%   $246.3378   $246.34   $246.35   $246.30  
  Purchase #7 $65.49   4.136%   $68.1987   $68.20   $68.20   $68.20  
  7 purchase totals = $1,144.68       $1,249.9447   $1,249.95   $1,249.95   $1,250.00