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	$66.42	12.746%	$74.8859	$74.89	$74.90	$74.90
Purchase #2	$188.40	8.601%	$204.6043	$204.60	$204.60	$204.60
Purchase #3	$54.58	4.237%	$56.8926	$56.89	$56.90	$56.90
Purchase #4	$107.65	10.160%	$118.5872	$118.59	$118.60	$118.60
Purchase #5	$85.97	5.804%	$90.9597	$90.96	$90.95	$91.00
Purchase #6	$85.72	5.587%	$90.5092	$90.51	$90.50	$90.50
Purchase #7	$72.93	6.595%	$77.7397	$77.74	$77.75	$77.70
7 purchase totals =	$661.67		$714.1786	$714.18	$714.20	$714.20