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 $49.49   13.568%   $56.2048   $56.20   $56.20   $56.20  
  Purchase #2 $173.94   4.765%   $182.2282   $182.23   $182.25   $182.20  
  Purchase #3 $89.32   9.798%   $98.0716   $98.07   $98.05   $98.10  
  Purchase #4 $88.38   3.719%   $91.6669   $91.67   $91.65   $91.70  
  Purchase #5 $55.55   10.306%   $61.275   $61.28   $61.30   $61.30  
  Purchase #6 $161.82   4.373%   $168.8964   $168.90   $168.90   $168.90  
  Purchase #7 $144.25   4.872%   $151.2779   $151.28   $151.30   $151.30  
  7 purchase totals = $762.75       $809.6208   $809.63   $809.65   $809.70