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	$235.51	7.323%	$252.7564	$252.76	$252.75	$252.80
Purchase #2	$112.34	13.858%	$127.9081	$127.91	$127.90	$127.90
Purchase #3	$231.37	10.741%	$256.2215	$256.22	$256.20	$256.20
Purchase #4	$72.98	13.594%	$82.9009	$82.90	$82.90	$82.90
Purchase #5	$185.76	5.128%	$195.2858	$195.29	$195.30	$195.30
Purchase #6	$163.67	5.136%	$172.0761	$172.08	$172.10	$172.10
Purchase #7	$44.68	13.221%	$50.5871	$50.59	$50.60	$50.60
7 purchase totals =	$1,046.31		$1,137.7359	$1,137.75	$1,137.75	$1,137.80