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	$236.74	8.162%	$256.0627	$256.06	$256.05	$256.10
Purchase #2	$108.88	10.766%	$120.602	$120.60	$120.60	$120.60
Purchase #3	$106.27	4.589%	$111.1467	$111.15	$111.15	$111.10
Purchase #4	$135.57	7.477%	$145.7066	$145.71	$145.70	$145.70
Purchase #5	$164.90	12.406%	$185.3575	$185.36	$185.35	$185.40
Purchase #6	$36.87	6.454%	$39.2496	$39.25	$39.25	$39.20
Purchase #7	$190.47	12.273%	$213.8464	$213.85	$213.85	$213.80
7 purchase totals =	$979.70		$1,071.9715	$1,071.98	$1,071.95	$1,071.90