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	$55.42	7.616%	$59.6408	$59.64	$59.65	$59.60
Purchase #2	$70.33	12.254%	$78.9482	$78.95	$78.95	$78.90
Purchase #3	$184.68	11.819%	$206.5073	$206.51	$206.50	$206.50
Purchase #4	$150.74	11.263%	$167.7178	$167.72	$167.70	$167.70
Purchase #5	$204.32	11.384%	$227.5798	$227.58	$227.60	$227.60
Purchase #6	$124.64	8.153%	$134.8019	$134.80	$134.80	$134.80
Purchase #7	$112.55	3.286%	$116.2484	$116.25	$116.25	$116.20
7 purchase totals =	$902.68		$991.4442	$991.45	$991.45	$991.30