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	$11.88	5.414%	$12.5232	$12.52	$12.50	$12.50
Purchase #2	$248.71	6.479%	$264.8239	$264.82	$264.80	$264.80
Purchase #3	$186.68	9.542%	$204.493	$204.49	$204.50	$204.50
Purchase #4	$101.90	9.114%	$111.1872	$111.19	$111.20	$111.20
Purchase #5	$54.66	12.698%	$61.6007	$61.60	$61.60	$61.60
Purchase #6	$66.64	7.837%	$71.8626	$71.86	$71.85	$71.90
Purchase #7	$130.28	11.409%	$145.1436	$145.14	$145.15	$145.10
7 purchase totals =	$800.75		$871.6342	$871.62	$871.60	$871.60