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	$62.69	7.158%	$67.1774	$67.18	$67.20	$67.20
Purchase #2	$16.91	10.435%	$18.6746	$18.67	$18.65	$18.70
Purchase #3	$10.77	11.831%	$12.0442	$12.04	$12.05	$12.00
Purchase #4	$7.26	7.516%	$7.8057	$7.81	$7.80	$7.80
Purchase #5	$109.92	10.492%	$121.4528	$121.45	$121.45	$121.50
Purchase #6	$44.73	13.397%	$50.7225	$50.72	$50.70	$50.70
Purchase #7	$38.54	11.194%	$42.8542	$42.85	$42.85	$42.90
7 purchase totals =	$290.82		$320.7314	$320.72	$320.70	$320.80