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	$6.31	12.486%	$7.0979	$7.10	$7.10	$7.10
Purchase #2	$17.95	7.215%	$19.2451	$19.25	$19.25	$19.20
Purchase #3	$99.77	11.775%	$111.5179	$111.52	$111.50	$111.50
Purchase #4	$215.41	5.687%	$227.6604	$227.66	$227.65	$227.70
Purchase #5	$100.55	4.636%	$105.2115	$105.21	$105.20	$105.20
Purchase #6	$12.90	6.493%	$13.7376	$13.74	$13.75	$13.70
Purchase #7	$237.72	12.776%	$268.0911	$268.09	$268.10	$268.10
7 purchase totals =	$690.61		$752.5615	$752.57	$752.55	$752.50