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 $240.95   8.734%   $261.9946   $261.99   $262.00   $262.00  
  Purchase #2 $87.92   7.700%   $94.6898   $94.69   $94.70   $94.70  
  Purchase #3 $14.71   10.170%   $16.206   $16.21   $16.20   $16.20  
  Purchase #4 $133.61   5.517%   $140.9813   $140.98   $141.00   $141.00  
  Purchase #5 $178.76   11.192%   $198.7668   $198.77   $198.75   $198.80  
  Purchase #6 $96.27   3.732%   $99.8628   $99.86   $99.85   $99.90  
  Purchase #7 $221.51   6.490%   $235.886   $235.89   $235.90   $235.90  
  7 purchase totals = $973.73       $1,048.3873   $1,048.39   $1,048.40   $1,048.50