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	$49.42	13.278%	$55.982	$55.98	$56.00	$56.00
Purchase #2	$20.26	6.594%	$21.5959	$21.60	$21.60	$21.60
Purchase #3	$36.64	9.405%	$40.086	$40.09	$40.10	$40.10
Purchase #4	$226.51	4.416%	$236.5127	$236.51	$236.50	$236.50
Purchase #5	$120.68	5.610%	$127.4501	$127.45	$127.45	$127.50
Purchase #6	$11.25	9.845%	$12.3576	$12.36	$12.35	$12.40
Purchase #7	$40.93	10.373%	$45.1757	$45.18	$45.20	$45.20
7 purchase totals =	$505.69		$539.1600	$539.17	$539.20	$539.30