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	$130.27	8.362%	$141.1632	$141.16	$141.15	$141.20
Purchase #2	$112.44	13.632%	$127.7678	$127.77	$127.75	$127.80
Purchase #3	$52.57	13.749%	$59.7978	$59.80	$59.80	$59.80
Purchase #4	$15.60	10.662%	$17.2633	$17.26	$17.25	$17.30
Purchase #5	$79.96	13.146%	$90.4715	$90.47	$90.45	$90.50
Purchase #6	$11.54	13.489%	$13.0966	$13.10	$13.10	$13.10
Purchase #7	$54.67	4.615%	$57.193	$57.19	$57.20	$57.20
7 purchase totals =	$457.05		$506.7532	$506.75	$506.70	$506.90