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	$143.41	10.730%	$158.7979	$158.80	$158.80	$158.80
Purchase #2	$57.81	8.719%	$62.8505	$62.85	$62.85	$62.90
Purchase #3	$227.44	12.694%	$256.3112	$256.31	$256.30	$256.30
Purchase #4	$11.83	7.654%	$12.7355	$12.74	$12.75	$12.70
Purchase #5	$167.26	9.676%	$183.4441	$183.44	$183.45	$183.40
Purchase #6	$102.93	8.567%	$111.748	$111.75	$111.75	$111.70
Purchase #7	$104.52	6.589%	$111.4068	$111.41	$111.40	$111.40
7 purchase totals =	$815.20		$897.2940	$897.30	$897.30	$897.20