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	$108.97	11.722%	$121.7435	$121.74	$121.75	$121.70
Purchase #2	$105.98	11.560%	$118.2313	$118.23	$118.25	$118.20
Purchase #3	$237.44	7.537%	$255.3359	$255.34	$255.35	$255.30
Purchase #4	$151.92	4.411%	$158.6212	$158.62	$158.60	$158.60
Purchase #5	$171.50	4.553%	$179.3084	$179.31	$179.30	$179.30
Purchase #6	$197.31	11.243%	$219.4936	$219.49	$219.50	$219.50
Purchase #7	$26.38	4.471%	$27.5594	$27.56	$27.55	$27.60
7 purchase totals =	$999.50		$1,080.2933	$1,080.29	$1,080.30	$1,080.20