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	$44.46	6.807%	$47.4864	$47.49	$47.50	$47.50
Purchase #2	$9.78	12.830%	$11.0348	$11.03	$11.05	$11.00
Purchase #3	$123.55	11.105%	$137.2702	$137.27	$137.25	$137.30
Purchase #4	$186.80	12.815%	$210.7384	$210.74	$210.75	$210.70
Purchase #5	$82.57	3.480%	$85.4434	$85.44	$85.45	$85.40
Purchase #6	$236.91	12.656%	$266.8933	$266.89	$266.90	$266.90
Purchase #7	$217.25	9.788%	$238.5144	$238.51	$238.50	$238.50
7 purchase totals =	$901.32		$997.3809	$997.37	$997.40	$997.30