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	$22.46	7.104%	$24.0556	$24.06	$24.05	$24.10
Purchase #2	$106.64	10.299%	$117.6229	$117.62	$117.60	$117.60
Purchase #3	$144.80	6.605%	$154.364	$154.36	$154.35	$154.40
Purchase #4	$71.60	8.707%	$77.8342	$77.83	$77.85	$77.80
Purchase #5	$112.84	13.314%	$127.8635	$127.86	$127.85	$127.90
Purchase #6	$50.59	7.415%	$54.3412	$54.34	$54.35	$54.30
Purchase #7	$109.89	5.778%	$116.2394	$116.24	$116.25	$116.20
7 purchase totals =	$618.82		$672.3208	$672.31	$672.30	$672.30