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	$158.39	3.736%	$164.3075	$164.31	$164.30	$164.30
Purchase #2	$240.90	10.640%	$266.5318	$266.53	$266.55	$266.50
Purchase #3	$163.45	5.835%	$172.9873	$172.99	$173.00	$173.00
Purchase #4	$40.52	12.307%	$45.5068	$45.51	$45.50	$45.50
Purchase #5	$18.47	11.638%	$20.6195	$20.62	$20.60	$20.60
Purchase #6	$12.64	3.576%	$13.092	$13.09	$13.10	$13.10
Purchase #7	$146.37	10.346%	$161.5134	$161.51	$161.50	$161.50
7 purchase totals =	$780.74		$844.5583	$844.56	$844.55	$844.50