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	$152.85	5.319%	$160.9801	$160.98	$161.00	$161.00
Purchase #2	$212.71	11.154%	$236.4357	$236.44	$236.45	$236.40
Purchase #3	$198.30	3.640%	$205.5181	$205.52	$205.50	$205.50
Purchase #4	$103.70	7.729%	$111.715	$111.72	$111.70	$111.70
Purchase #5	$24.82	9.476%	$27.1719	$27.17	$27.15	$27.20
Purchase #6	$9.98	10.575%	$11.0354	$11.04	$11.05	$11.00
Purchase #7	$207.46	8.640%	$225.3845	$225.38	$225.40	$225.40
7 purchase totals =	$909.82		$978.2407	$978.25	$978.25	$978.20