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	$61.34	8.348%	$66.4607	$66.46	$66.45	$66.50
Purchase #2	$153.29	3.242%	$158.2597	$158.26	$158.25	$158.30
Purchase #3	$61.83	5.254%	$65.0785	$65.08	$65.10	$65.10
Purchase #4	$39.76	11.620%	$44.3801	$44.38	$44.40	$44.40
Purchase #5	$101.25	13.212%	$114.6272	$114.63	$114.65	$114.60
Purchase #6	$234.85	10.191%	$258.7836	$258.78	$258.80	$258.80
Purchase #7	$52.46	8.114%	$56.7166	$56.72	$56.70	$56.70
7 purchase totals =	$704.78		$764.3064	$764.31	$764.35	$764.40