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	$123.71	12.567%	$139.2566	$139.26	$139.25	$139.30
Purchase #2	$144.59	6.258%	$153.6384	$153.64	$153.65	$153.60
Purchase #3	$108.58	3.813%	$112.7202	$112.72	$112.70	$112.70
Purchase #4	$107.60	11.247%	$119.7018	$119.70	$119.70	$119.70
Purchase #5	$60.67	3.392%	$62.7279	$62.73	$62.75	$62.70
Purchase #6	$34.53	11.143%	$38.3777	$38.38	$38.40	$38.40
Purchase #7	$101.27	10.416%	$111.8183	$111.82	$111.80	$111.80
7 purchase totals =	$680.95		$738.2409	$738.25	$738.25	$738.20