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 $209.48   6.593%   $223.291   $223.29   $223.30   $223.30  
  Purchase #2 $215.66   12.226%   $242.0266   $242.03   $242.05   $242.00  
  Purchase #3 $242.45   11.466%   $270.2493   $270.25   $270.25   $270.20  
  Purchase #4 $229.53   13.874%   $261.375   $261.38   $261.40   $261.40  
  Purchase #5 $245.31   6.691%   $261.7237   $261.72   $261.70   $261.70  
  Purchase #6 $134.55   12.754%   $151.7105   $151.71   $151.70   $151.70  
  Purchase #7 $52.51   8.401%   $56.9214   $56.92   $56.90   $56.90  
  7 purchase totals = $1,329.49       $1,467.2975   $1,467.30   $1,467.30   $1,467.20