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	$97.60	11.474%	$108.7986	$108.80	$108.80	$108.80
Purchase #2	$88.93	12.615%	$100.1485	$100.15	$100.15	$100.10
Purchase #3	$18.76	5.763%	$19.8411	$19.84	$19.85	$19.80
Purchase #4	$105.69	9.592%	$115.8278	$115.83	$115.85	$115.80
Purchase #5	$25.80	11.161%	$28.6795	$28.68	$28.70	$28.70
Purchase #6	$9.78	13.449%	$11.0953	$11.10	$11.10	$11.10
Purchase #7	$187.56	4.698%	$196.3716	$196.37	$196.35	$196.40
7 purchase totals =	$534.12		$580.7624	$580.77	$580.80	$580.70