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	$59.93	13.339%	$67.9241	$67.92	$67.90	$67.90
Purchase #2	$141.77	3.273%	$146.4101	$146.41	$146.40	$146.40
Purchase #3	$47.36	7.405%	$50.867	$50.87	$50.85	$50.90
Purchase #4	$197.28	12.338%	$221.6204	$221.62	$221.60	$221.60
Purchase #5	$233.42	3.210%	$240.9128	$240.91	$240.90	$240.90
Purchase #6	$239.27	5.133%	$251.5517	$251.55	$251.55	$251.60
Purchase #7	$99.65	11.530%	$111.1396	$111.14	$111.15	$111.10
7 purchase totals =	$1,018.68		$1,090.4257	$1,090.42	$1,090.35	$1,090.40