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	$115.29	5.492%	$121.6217	$121.62	$121.60	$121.60
Purchase #2	$70.31	11.525%	$78.4132	$78.41	$78.40	$78.40
Purchase #3	$106.32	3.195%	$109.7169	$109.72	$109.70	$109.70
Purchase #4	$72.88	9.433%	$79.7548	$79.75	$79.75	$79.80
Purchase #5	$109.41	6.808%	$116.8586	$116.86	$116.85	$116.90
Purchase #6	$59.49	4.348%	$62.0766	$62.08	$62.10	$62.10
Purchase #7	$151.36	12.667%	$170.5328	$170.53	$170.55	$170.50
7 purchase totals =	$685.06		$738.9746	$738.97	$738.95	$739.00