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	$104.35	12.205%	$117.0859	$117.09	$117.10	$117.10
Purchase #2	$17.87	12.170%	$20.0448	$20.04	$20.05	$20.00
Purchase #3	$188.48	6.308%	$200.3693	$200.37	$200.35	$200.40
Purchase #4	$120.89	8.605%	$131.2926	$131.29	$131.30	$131.30
Purchase #5	$194.72	11.684%	$217.4711	$217.47	$217.45	$217.50
Purchase #6	$179.47	4.817%	$188.1151	$188.12	$188.10	$188.10
Purchase #7	$72.64	6.303%	$77.2185	$77.22	$77.20	$77.20
7 purchase totals =	$878.42		$951.5973	$951.60	$951.55	$951.60