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	$99.32	12.341%	$111.5771	$111.58	$111.60	$111.60
Purchase #2	$76.67	9.234%	$83.7497	$83.75	$83.75	$83.70
Purchase #3	$168.92	10.540%	$186.7242	$186.72	$186.70	$186.70
Purchase #4	$65.82	11.447%	$73.3544	$73.35	$73.35	$73.40
Purchase #5	$243.32	13.398%	$275.92	$275.92	$275.90	$275.90
Purchase #6	$99.53	8.755%	$108.2439	$108.24	$108.25	$108.20
Purchase #7	$51.95	9.233%	$56.7465	$56.75	$56.75	$56.70
7 purchase totals =	$805.53		$896.3158	$896.31	$896.30	$896.20