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	$124.45	3.167%	$128.3913	$128.39	$128.40	$128.40
Purchase #2	$233.46	11.247%	$259.7172	$259.72	$259.70	$259.70
Purchase #3	$109.28	3.292%	$112.8775	$112.88	$112.90	$112.90
Purchase #4	$112.66	13.188%	$127.5176	$127.52	$127.50	$127.50
Purchase #5	$44.31	7.763%	$47.7498	$47.75	$47.75	$47.70
Purchase #6	$217.26	5.772%	$229.8002	$229.80	$229.80	$229.80
Purchase #7	$10.33	5.420%	$10.8899	$10.89	$10.90	$10.90
7 purchase totals =	$851.75		$916.9435	$916.95	$916.95	$916.90