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 $234.51   11.752%   $262.0696   $262.07   $262.05   $262.10  
  Purchase #2 $119.59   5.827%   $126.5585   $126.56   $126.55   $126.60  
  Purchase #3 $72.80   10.131%   $80.1754   $80.18   $80.20   $80.20  
  Purchase #4 $238.38   10.133%   $262.535   $262.54   $262.55   $262.50  
  Purchase #5 $80.41   5.704%   $84.9966   $85.00   $85.00   $85.00  
  Purchase #6 $88.42   4.354%   $92.2698   $92.27   $92.25   $92.30  
  Purchase #7 $57.97   4.559%   $60.6129   $60.61   $60.60   $60.60  
  7 purchase totals = $892.08       $969.2178   $969.23   $969.20   $969.30