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	$60.80	9.412%	$66.5225	$66.52	$66.50	$66.50
Purchase #2	$200.53	13.765%	$228.133	$228.13	$228.15	$228.10
Purchase #3	$46.54	4.296%	$48.5394	$48.54	$48.55	$48.50
Purchase #4	$19.40	7.123%	$20.7819	$20.78	$20.80	$20.80
Purchase #5	$206.82	4.314%	$215.7422	$215.74	$215.75	$215.70
Purchase #6	$48.30	12.852%	$54.5075	$54.51	$54.50	$54.50
Purchase #7	$67.74	11.266%	$75.3716	$75.37	$75.35	$75.40
7 purchase totals =	$650.13		$709.5981	$709.59	$709.60	$709.50