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	$63.85	4.603%	$66.789	$66.79	$66.80	$66.80
Purchase #2	$186.42	12.308%	$209.3646	$209.36	$209.35	$209.40
Purchase #3	$16.87	4.399%	$17.6121	$17.61	$17.60	$17.60
Purchase #4	$156.54	6.369%	$166.51	$166.51	$166.50	$166.50
Purchase #5	$19.61	11.402%	$21.8459	$21.85	$21.85	$21.80
Purchase #6	$128.25	6.396%	$136.4529	$136.45	$136.45	$136.50
Purchase #7	$68.27	5.202%	$71.8214	$71.82	$71.80	$71.80
7 purchase totals =	$639.81		$690.3959	$690.39	$690.35	$690.40