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	$17.70	7.803%	$19.0811	$19.08	$19.10	$19.10
Purchase #2	$80.55	3.511%	$83.3781	$83.38	$83.40	$83.40
Purchase #3	$142.42	11.386%	$158.6359	$158.64	$158.65	$158.60
Purchase #4	$131.72	11.124%	$146.3725	$146.37	$146.35	$146.40
Purchase #5	$134.52	8.240%	$145.6044	$145.60	$145.60	$145.60
Purchase #6	$75.38	8.698%	$81.9366	$81.94	$81.95	$81.90
Purchase #7	$145.54	13.521%	$165.2185	$165.22	$165.20	$165.20
7 purchase totals =	$727.83		$800.2271	$800.23	$800.25	$800.20