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 $235.59   11.463%   $262.5957   $262.60   $262.60   $262.60  
  Purchase #2 $239.87   7.546%   $257.9706   $257.97   $257.95   $258.00  
  Purchase #3 $165.98   6.815%   $177.2915   $177.29   $177.30   $177.30  
  Purchase #4 $6.27   10.418%   $6.9232   $6.92   $6.90   $6.90  
  Purchase #5 $175.46   9.348%   $191.862   $191.86   $191.85   $191.90  
  Purchase #6 $249.62   12.389%   $280.5454   $280.55   $280.55   $280.50  
  Purchase #7 $114.50   8.652%   $124.4065   $124.41   $124.40   $124.40  
  7 purchase totals = $1,187.29       $1,301.5949   $1,301.60   $1,301.55   $1,301.60