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 $215.32   8.169%   $232.9095   $232.91   $232.90   $232.90  
  Purchase #2 $230.50   13.532%   $261.6913   $261.69   $261.70   $261.70  
  Purchase #3 $71.36   9.116%   $77.8652   $77.87   $77.85   $77.90  
  Purchase #4 $233.89   6.862%   $249.9395   $249.94   $249.95   $249.90  
  Purchase #5 $248.50   6.824%   $265.4576   $265.46   $265.45   $265.50  
  Purchase #6 $41.78   11.329%   $46.5133   $46.51   $46.50   $46.50  
  Purchase #7 $165.36   9.766%   $181.5091   $181.51   $181.50   $181.50  
  7 purchase totals = $1,206.71       $1,315.8855   $1,315.89   $1,315.85   $1,315.90