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	$34.96	9.657%	$38.3361	$38.34	$38.35	$38.30
Purchase #2	$212.65	8.436%	$230.5892	$230.59	$230.60	$230.60
Purchase #3	$249.82	5.563%	$263.7175	$263.72	$263.70	$263.70
Purchase #4	$142.45	11.297%	$158.5426	$158.54	$158.55	$158.50
Purchase #5	$80.80	12.532%	$90.9259	$90.93	$90.95	$90.90
Purchase #6	$44.29	13.770%	$50.3887	$50.39	$50.40	$50.40
Purchase #7	$166.75	4.639%	$174.4855	$174.49	$174.50	$174.50
7 purchase totals =	$931.72		$1,006.9855	$1,007.00	$1,007.05	$1,006.90