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	$44.77	10.811%	$49.6101	$49.61	$49.60	$49.60
Purchase #2	$118.62	7.667%	$127.7146	$127.71	$127.70	$127.70
Purchase #3	$117.91	9.261%	$128.8296	$128.83	$128.85	$128.80
Purchase #4	$137.51	13.313%	$155.8167	$155.82	$155.80	$155.80
Purchase #5	$21.69	13.363%	$24.5884	$24.59	$24.60	$24.60
Purchase #6	$172.45	9.292%	$188.4741	$188.47	$188.45	$188.50
Purchase #7	$97.68	5.711%	$103.2585	$103.26	$103.25	$103.30
7 purchase totals =	$710.63		$778.2920	$778.29	$778.25	$778.30