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	$73.57	9.221%	$80.3539	$80.35	$80.35	$80.40
Purchase #2	$107.77	3.574%	$111.6217	$111.62	$111.60	$111.60
Purchase #3	$89.85	6.790%	$95.9508	$95.95	$95.95	$96.00
Purchase #4	$132.97	4.702%	$139.2222	$139.22	$139.20	$139.20
Purchase #5	$51.37	8.405%	$55.6876	$55.69	$55.70	$55.70
Purchase #6	$122.27	7.791%	$131.7961	$131.80	$131.80	$131.80
Purchase #7	$45.78	9.682%	$50.2124	$50.21	$50.20	$50.20
7 purchase totals =	$623.58		$664.8447	$664.84	$664.80	$664.90