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	$29.60	6.815%	$31.6172	$31.62	$31.60	$31.60
Purchase #2	$64.55	12.718%	$72.7595	$72.76	$72.75	$72.80
Purchase #3	$27.43	8.778%	$29.8378	$29.84	$29.85	$29.80
Purchase #4	$106.37	10.389%	$117.4208	$117.42	$117.40	$117.40
Purchase #5	$151.89	8.546%	$164.8705	$164.87	$164.85	$164.90
Purchase #6	$33.68	13.514%	$38.2315	$38.23	$38.25	$38.20
Purchase #7	$128.30	7.114%	$137.4273	$137.43	$137.45	$137.40
7 purchase totals =	$541.82		$592.1646	$592.17	$592.15	$592.10