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	$100.25	13.296%	$113.5792	$113.58	$113.60	$113.60
Purchase #2	$231.91	10.617%	$256.5319	$256.53	$256.55	$256.50
Purchase #3	$17.39	10.336%	$19.1874	$19.19	$19.20	$19.20
Purchase #4	$115.45	13.596%	$131.1466	$131.15	$131.15	$131.10
Purchase #5	$101.74	6.222%	$108.0703	$108.07	$108.05	$108.10
Purchase #6	$117.54	8.340%	$127.3428	$127.34	$127.35	$127.30
Purchase #7	$155.71	9.231%	$170.0836	$170.08	$170.10	$170.10
7 purchase totals =	$839.99		$925.9418	$925.94	$926.00	$925.90