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	$18.44	13.298%	$20.8922	$20.89	$20.90	$20.90
Purchase #2	$236.52	9.470%	$258.9184	$258.92	$258.90	$258.90
Purchase #3	$70.25	11.852%	$78.576	$78.58	$78.60	$78.60
Purchase #4	$11.70	10.794%	$12.9629	$12.96	$12.95	$13.00
Purchase #5	$139.74	13.202%	$158.1885	$158.19	$158.20	$158.20
Purchase #6	$205.60	13.647%	$233.6582	$233.66	$233.65	$233.70
Purchase #7	$145.45	9.175%	$158.795	$158.80	$158.80	$158.80
7 purchase totals =	$827.70		$921.9912	$922.00	$922.00	$922.10