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	$18.44	9.782%	$20.2438	$20.24	$20.25	$20.20
Purchase #2	$56.42	10.416%	$62.2967	$62.30	$62.30	$62.30
Purchase #3	$126.44	13.486%	$143.4917	$143.49	$143.50	$143.50
Purchase #4	$96.51	4.239%	$100.6011	$100.60	$100.60	$100.60
Purchase #5	$61.85	13.773%	$70.3686	$70.37	$70.35	$70.40
Purchase #6	$59.31	10.393%	$65.4741	$65.47	$65.45	$65.50
Purchase #7	$216.94	8.611%	$235.6207	$235.62	$235.60	$235.60
7 purchase totals =	$635.91		$698.0967	$698.09	$698.05	$698.10