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	$160.31	7.702%	$172.6571	$172.66	$172.65	$172.70
Purchase #2	$111.85	7.585%	$120.3338	$120.33	$120.35	$120.30
Purchase #3	$127.45	9.618%	$139.7081	$139.71	$139.70	$139.70
Purchase #4	$103.47	7.485%	$111.2147	$111.21	$111.20	$111.20
Purchase #5	$45.58	4.252%	$47.5181	$47.52	$47.50	$47.50
Purchase #6	$63.67	6.410%	$67.7512	$67.75	$67.75	$67.80
Purchase #7	$153.82	3.147%	$158.6607	$158.66	$158.65	$158.70
7 purchase totals =	$766.15		$817.8437	$817.84	$817.80	$817.90