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	$10.25	11.691%	$11.4483	$11.45	$11.45	$11.40
Purchase #2	$227.88	9.191%	$248.8245	$248.82	$248.80	$248.80
Purchase #3	$249.44	8.852%	$271.5204	$271.52	$271.50	$271.50
Purchase #4	$241.99	13.286%	$274.1408	$274.14	$274.15	$274.10
Purchase #5	$116.37	9.777%	$127.7475	$127.75	$127.75	$127.70
Purchase #6	$33.32	12.798%	$37.5843	$37.58	$37.60	$37.60
Purchase #7	$43.40	4.476%	$45.3426	$45.34	$45.35	$45.30
7 purchase totals =	$922.65		$1,016.6084	$1,016.60	$1,016.60	$1,016.40