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	$80.69	11.747%	$90.1687	$90.17	$90.15	$90.20
Purchase #2	$218.93	5.546%	$231.0719	$231.07	$231.05	$231.10
Purchase #3	$118.48	7.615%	$127.5023	$127.50	$127.50	$127.50
Purchase #4	$114.26	8.606%	$124.0932	$124.09	$124.10	$124.10
Purchase #5	$13.50	5.748%	$14.276	$14.28	$14.30	$14.30
Purchase #6	$129.67	7.346%	$139.1956	$139.20	$139.20	$139.20
Purchase #7	$153.78	3.297%	$158.8501	$158.85	$158.85	$158.90
7 purchase totals =	$829.31		$885.1578	$885.16	$885.15	$885.30