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	$98.93	12.470%	$111.2666	$111.27	$111.25	$111.30
Purchase #2	$239.46	5.205%	$251.9239	$251.92	$251.90	$251.90
Purchase #3	$90.29	4.514%	$94.3657	$94.37	$94.35	$94.40
Purchase #4	$149.28	8.823%	$162.451	$162.45	$162.45	$162.50
Purchase #5	$103.84	13.779%	$118.1481	$118.15	$118.15	$118.10
Purchase #6	$166.36	4.299%	$173.5118	$173.51	$173.50	$173.50
Purchase #7	$250.75	11.304%	$279.0948	$279.09	$279.10	$279.10
7 purchase totals =	$1,098.91		$1,190.7619	$1,190.76	$1,190.70	$1,190.80