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	$85.45	3.832%	$88.7244	$88.72	$88.70	$88.70
Purchase #2	$42.32	7.715%	$45.585	$45.59	$45.60	$45.60
Purchase #3	$140.82	4.217%	$146.7584	$146.76	$146.75	$146.80
Purchase #4	$62.31	7.276%	$66.8437	$66.84	$66.85	$66.80
Purchase #5	$121.58	8.514%	$131.9313	$131.93	$131.95	$131.90
Purchase #6	$54.56	3.341%	$56.3828	$56.38	$56.40	$56.40
Purchase #7	$63.26	10.721%	$70.0421	$70.04	$70.05	$70.00
7 purchase totals =	$570.30		$606.2677	$606.26	$606.30	$606.20