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	$12.50	4.504%	$13.063	$13.06	$13.05	$13.10
Purchase #2	$221.60	8.579%	$240.6111	$240.61	$240.60	$240.60
Purchase #3	$114.72	13.768%	$130.5146	$130.51	$130.50	$130.50
Purchase #4	$146.51	13.183%	$165.8244	$165.82	$165.80	$165.80
Purchase #5	$146.39	7.213%	$156.9491	$156.95	$156.95	$156.90
Purchase #6	$28.40	7.255%	$30.4604	$30.46	$30.45	$30.50
Purchase #7	$90.60	10.509%	$100.1212	$100.12	$100.10	$100.10
7 purchase totals =	$760.72		$837.5438	$837.53	$837.45	$837.50