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 $52.63   10.228%   $58.013   $58.01   $58.00   $58.00  
  Purchase #2 $58.70   8.451%   $63.6607   $63.66   $63.65   $63.70  
  Purchase #3 $246.63   6.208%   $261.9408   $261.94   $261.95   $261.90  
  Purchase #4 $119.41   11.462%   $133.0968   $133.10   $133.10   $133.10  
  Purchase #5 $15.54   11.185%   $17.2781   $17.28   $17.30   $17.30  
  Purchase #6 $124.71   12.747%   $140.6068   $140.61   $140.60   $140.60  
  Purchase #7 $188.27   5.555%   $198.7284   $198.73   $198.75   $198.70  
  7 purchase totals = $805.89       $873.3246   $873.33   $873.35   $873.30