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	$163.71	9.654%	$179.5146	$179.51	$179.50	$179.50
Purchase #2	$220.73	6.680%	$235.4748	$235.47	$235.45	$235.50
Purchase #3	$126.82	13.843%	$144.3757	$144.38	$144.40	$144.40
Purchase #4	$77.46	5.720%	$81.8907	$81.89	$81.90	$81.90
Purchase #5	$115.91	6.826%	$123.822	$123.82	$123.80	$123.80
Purchase #6	$241.45	12.176%	$270.849	$270.85	$270.85	$270.80
Purchase #7	$214.37	8.117%	$231.7704	$231.77	$231.75	$231.80
7 purchase totals =	$1,160.45		$1,267.6972	$1,267.69	$1,267.65	$1,267.70