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	$32.31	5.659%	$34.1384	$34.14	$34.15	$34.10
Purchase #2	$118.29	11.537%	$131.9371	$131.94	$131.95	$131.90
Purchase #3	$44.82	11.271%	$49.8717	$49.87	$49.85	$49.90
Purchase #4	$19.66	11.481%	$21.9172	$21.92	$21.90	$21.90
Purchase #5	$56.32	9.331%	$61.5752	$61.58	$61.60	$61.60
Purchase #6	$207.59	6.638%	$221.3698	$221.37	$221.35	$221.40
Purchase #7	$16.32	6.225%	$17.3359	$17.34	$17.35	$17.30
7 purchase totals =	$495.31		$538.1453	$538.16	$538.15	$538.10