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	$25.44	9.492%	$27.8548	$27.85	$27.85	$27.90
Purchase #2	$245.51	4.862%	$257.4467	$257.45	$257.45	$257.40
Purchase #3	$222.60	10.454%	$245.8706	$245.87	$245.85	$245.90
Purchase #4	$105.72	10.569%	$116.8935	$116.89	$116.90	$116.90
Purchase #5	$205.87	13.297%	$233.2445	$233.24	$233.25	$233.20
Purchase #6	$20.60	12.750%	$23.2265	$23.23	$23.25	$23.20
Purchase #7	$59.69	3.501%	$61.7797	$61.78	$61.80	$61.80
7 purchase totals =	$885.43		$966.3163	$966.31	$966.35	$966.30