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	$89.39	5.159%	$94.0016	$94.00	$94.00	$94.00
Purchase #2	$154.31	12.288%	$173.2716	$173.27	$173.25	$173.30
Purchase #3	$22.75	4.305%	$23.7294	$23.73	$23.75	$23.70
Purchase #4	$50.64	11.346%	$56.3856	$56.39	$56.40	$56.40
Purchase #5	$99.66	12.639%	$112.256	$112.26	$112.25	$112.30
Purchase #6	$86.26	4.741%	$90.3496	$90.35	$90.35	$90.30
Purchase #7	$148.53	13.593%	$168.7197	$168.72	$168.70	$168.70
7 purchase totals =	$651.54		$718.7135	$718.72	$718.70	$718.70