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	$122.40	11.218%	$136.1308	$136.13	$136.15	$136.10
Purchase #2	$74.56	10.415%	$82.3254	$82.33	$82.35	$82.30
Purchase #3	$247.85	12.141%	$277.9415	$277.94	$277.95	$277.90
Purchase #4	$166.66	3.718%	$172.8564	$172.86	$172.85	$172.90
Purchase #5	$46.78	7.383%	$50.2338	$50.23	$50.25	$50.20
Purchase #6	$241.74	12.758%	$272.5812	$272.58	$272.60	$272.60
Purchase #7	$9.98	7.663%	$10.7448	$10.74	$10.75	$10.70
7 purchase totals =	$909.97		$1,002.8139	$1,002.81	$1,002.90	$1,002.70