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	$138.37	7.318%	$148.4959	$148.50	$148.50	$148.50
Purchase #2	$211.52	5.493%	$223.1388	$223.14	$223.15	$223.10
Purchase #3	$144.29	6.467%	$153.6212	$153.62	$153.60	$153.60
Purchase #4	$9.39	9.636%	$10.2948	$10.29	$10.30	$10.30
Purchase #5	$175.95	7.109%	$188.4583	$188.46	$188.45	$188.50
Purchase #6	$49.41	5.782%	$52.2669	$52.27	$52.25	$52.30
Purchase #7	$38.51	12.189%	$43.204	$43.20	$43.20	$43.20
7 purchase totals =	$767.44		$819.4799	$819.48	$819.45	$819.50