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	$173.87	8.201%	$188.1291	$188.13	$188.15	$188.10
Purchase #2	$50.46	4.303%	$52.6313	$52.63	$52.65	$52.60
Purchase #3	$229.40	10.623%	$253.7692	$253.77	$253.75	$253.80
Purchase #4	$49.57	13.835%	$56.428	$56.43	$56.45	$56.40
Purchase #5	$220.89	13.590%	$250.909	$250.91	$250.90	$250.90
Purchase #6	$230.90	9.181%	$252.0989	$252.10	$252.10	$252.10
Purchase #7	$36.72	11.406%	$40.9083	$40.91	$40.90	$40.90
7 purchase totals =	$991.81		$1,094.8738	$1,094.88	$1,094.90	$1,094.80