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 $131.94   8.203%   $142.763   $142.76   $142.75   $142.80  
  Purchase #2 $17.66   13.215%   $19.9938   $19.99   $20.00   $20.00  
  Purchase #3 $88.47   4.490%   $92.4423   $92.44   $92.45   $92.40  
  Purchase #4 $76.92   8.436%   $83.409   $83.41   $83.40   $83.40  
  Purchase #5 $200.72   6.139%   $213.0422   $213.04   $213.05   $213.00  
  Purchase #6 $136.66   10.532%   $151.053   $151.05   $151.05   $151.10  
  Purchase #7 $20.80   11.817%   $23.2579   $23.26   $23.25   $23.30  
  7 purchase totals = $673.17       $725.9612   $725.95   $725.95   $726.00