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	$141.30	10.499%	$156.1351	$156.14	$156.15	$156.10
Purchase #2	$109.78	7.108%	$117.5832	$117.58	$117.60	$117.60
Purchase #3	$18.64	9.737%	$20.455	$20.46	$20.45	$20.50
Purchase #4	$99.45	4.237%	$103.6637	$103.66	$103.65	$103.70
Purchase #5	$91.77	6.445%	$97.6846	$97.68	$97.70	$97.70
Purchase #6	$172.80	13.520%	$196.1626	$196.16	$196.15	$196.20
Purchase #7	$116.56	6.406%	$124.0268	$124.03	$124.05	$124.00
7 purchase totals =	$750.30		$815.7110	$815.71	$815.75	$815.80