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	$28.80	6.233%	$30.5951	$30.60	$30.60	$30.60
Purchase #2	$213.27	10.543%	$235.7551	$235.76	$235.75	$235.80
Purchase #3	$17.97	4.521%	$18.7824	$18.78	$18.80	$18.80
Purchase #4	$195.45	13.784%	$222.3908	$222.39	$222.40	$222.40
Purchase #5	$97.67	10.208%	$107.6402	$107.64	$107.65	$107.60
Purchase #6	$168.73	12.737%	$190.2211	$190.22	$190.20	$190.20
Purchase #7	$82.87	9.159%	$90.4601	$90.46	$90.45	$90.50
7 purchase totals =	$804.76		$895.8448	$895.85	$895.85	$895.90