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 $245.54   6.647%   $261.861   $261.86   $261.85   $261.90  
  Purchase #2 $125.86   3.292%   $130.0033   $130.00   $130.00   $130.00  
  Purchase #3 $60.88   9.683%   $66.775   $66.78   $66.80   $66.80  
  Purchase #4 $154.29   3.235%   $159.2813   $159.28   $159.30   $159.30  
  Purchase #5 $240.97   4.294%   $251.3173   $251.32   $251.30   $251.30  
  Purchase #6 $52.53   4.640%   $54.9674   $54.97   $54.95   $55.00  
  Purchase #7 $26.94   13.615%   $30.6079   $30.61   $30.60   $30.60  
  7 purchase totals = $907.01       $954.8132   $954.82   $954.80   $954.90