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 $189.42   13.526%   $215.0409   $215.04   $215.05   $215.00  
  Purchase #2 $130.94   10.717%   $144.9728   $144.97   $144.95   $145.00  
  Purchase #3 $84.87   8.711%   $92.263   $92.26   $92.25   $92.30  
  Purchase #4 $94.33   9.214%   $103.0216   $103.02   $103.00   $103.00  
  Purchase #5 $117.69   11.577%   $131.315   $131.32   $131.30   $131.30  
  Purchase #6 $15.93   3.343%   $16.4625   $16.46   $16.45   $16.50  
  Purchase #7 $32.38   11.165%   $35.9952   $36.00   $36.00   $36.00  
  7 purchase totals = $665.56       $739.0710   $739.07   $739.00   $739.10