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	$45.52	12.193%	$51.0703	$51.07	$51.05	$51.10
Purchase #2	$17.62	7.114%	$18.8735	$18.87	$18.85	$18.90
Purchase #3	$176.27	4.110%	$183.5147	$183.51	$183.50	$183.50
Purchase #4	$176.41	5.388%	$185.915	$185.92	$185.90	$185.90
Purchase #5	$127.51	12.664%	$143.6579	$143.66	$143.65	$143.70
Purchase #6	$70.45	10.475%	$77.8296	$77.83	$77.85	$77.80
Purchase #7	$116.69	10.545%	$128.995	$129.00	$129.00	$129.00
7 purchase totals =	$730.47		$789.8560	$789.86	$789.80	$789.90