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 $213.89   13.120%   $241.9524   $241.95   $241.95   $242.00  
  Purchase #2 $245.66   6.574%   $261.8097   $261.81   $261.80   $261.80  
  Purchase #3 $96.64   7.242%   $103.6387   $103.64   $103.65   $103.60  
  Purchase #4 $54.77   6.413%   $58.2824   $58.28   $58.30   $58.30  
  Purchase #5 $122.64   6.705%   $130.863   $130.86   $130.85   $130.90  
  Purchase #6 $113.99   10.629%   $126.106   $126.11   $126.10   $126.10  
  Purchase #7 $117.41   7.522%   $126.2416   $126.24   $126.25   $126.20  
  7 purchase totals = $965.00       $1,048.8938   $1,048.89   $1,048.90   $1,048.90