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	$84.50	6.415%	$89.9207	$89.92	$89.90	$89.90
Purchase #2	$80.60	10.247%	$88.8591	$88.86	$88.85	$88.90
Purchase #3	$132.50	9.461%	$145.0358	$145.04	$145.05	$145.00
Purchase #4	$154.49	11.542%	$172.3212	$172.32	$172.30	$172.30
Purchase #5	$20.47	5.534%	$21.6028	$21.60	$21.60	$21.60
Purchase #6	$94.91	4.404%	$99.0898	$99.09	$99.10	$99.10
Purchase #7	$240.93	10.186%	$265.4711	$265.47	$265.45	$265.50
7 purchase totals =	$808.40		$882.3005	$882.30	$882.25	$882.30