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	$217.96	10.247%	$240.2944	$240.29	$240.30	$240.30
Purchase #2	$18.70	3.471%	$19.3491	$19.35	$19.35	$19.30
Purchase #3	$47.73	6.205%	$50.6916	$50.69	$50.70	$50.70
Purchase #4	$12.90	11.833%	$14.4265	$14.43	$14.45	$14.40
Purchase #5	$111.52	10.731%	$123.4872	$123.49	$123.50	$123.50
Purchase #6	$116.34	10.786%	$128.8884	$128.89	$128.90	$128.90
Purchase #7	$56.99	8.479%	$61.8222	$61.82	$61.80	$61.80
7 purchase totals =	$582.14		$638.9594	$638.96	$639.00	$638.90