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	$142.72	8.384%	$154.6856	$154.69	$154.70	$154.70
Purchase #2	$20.83	6.298%	$22.1419	$22.14	$22.15	$22.10
Purchase #3	$120.65	13.109%	$136.466	$136.47	$136.45	$136.50
Purchase #4	$72.73	8.166%	$78.6691	$78.67	$78.65	$78.70
Purchase #5	$29.77	3.613%	$30.8456	$30.85	$30.85	$30.80
Purchase #6	$124.50	5.288%	$131.0836	$131.08	$131.10	$131.10
Purchase #7	$6.90	12.429%	$7.7576	$7.76	$7.75	$7.80
7 purchase totals =	$518.10		$561.6494	$561.66	$561.65	$561.70