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	$198.41	13.310%	$224.8184	$224.82	$224.80	$224.80
Purchase #2	$68.51	6.160%	$72.7302	$72.73	$72.75	$72.70
Purchase #3	$151.70	13.741%	$172.5451	$172.55	$172.55	$172.50
Purchase #4	$120.86	5.231%	$127.1822	$127.18	$127.20	$127.20
Purchase #5	$47.86	9.245%	$52.2847	$52.28	$52.30	$52.30
Purchase #6	$66.48	3.668%	$68.9185	$68.92	$68.90	$68.90
Purchase #7	$230.79	10.527%	$255.0853	$255.09	$255.10	$255.10
7 purchase totals =	$884.61		$973.5644	$973.57	$973.60	$973.50