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	$12.28	3.790%	$12.7454	$12.75	$12.75	$12.70
Purchase #2	$236.49	4.781%	$247.7966	$247.80	$247.80	$247.80
Purchase #3	$221.79	13.139%	$250.931	$250.93	$250.95	$250.90
Purchase #4	$115.88	6.504%	$123.4168	$123.42	$123.40	$123.40
Purchase #5	$129.39	10.373%	$142.8116	$142.81	$142.80	$142.80
Purchase #6	$45.60	7.126%	$48.8495	$48.85	$48.85	$48.80
Purchase #7	$176.86	7.782%	$190.6232	$190.62	$190.60	$190.60
7 purchase totals =	$938.29		$1,017.1741	$1,017.18	$1,017.15	$1,017.00