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	$159.94	8.378%	$173.3398	$173.34	$173.35	$173.30
Purchase #2	$221.98	4.383%	$231.7094	$231.71	$231.70	$231.70
Purchase #3	$111.99	10.308%	$123.5339	$123.53	$123.55	$123.50
Purchase #4	$49.77	5.115%	$52.3157	$52.32	$52.30	$52.30
Purchase #5	$111.66	13.808%	$127.078	$127.08	$127.10	$127.10
Purchase #6	$131.64	11.369%	$146.6062	$146.61	$146.60	$146.60
Purchase #7	$108.81	9.849%	$119.5267	$119.53	$119.55	$119.50
7 purchase totals =	$895.79		$974.1097	$974.12	$974.15	$974.00