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	$26.82	10.438%	$29.6195	$29.62	$29.60	$29.60
Purchase #2	$9.47	4.464%	$9.8927	$9.89	$9.90	$9.90
Purchase #3	$232.87	10.292%	$256.837	$256.84	$256.85	$256.80
Purchase #4	$233.87	9.441%	$255.9497	$255.95	$255.95	$255.90
Purchase #5	$55.52	7.461%	$59.6623	$59.66	$59.65	$59.70
Purchase #6	$90.25	11.426%	$100.562	$100.56	$100.55	$100.60
Purchase #7	$178.97	9.536%	$196.0366	$196.04	$196.05	$196.00
7 purchase totals =	$827.77		$908.5598	$908.56	$908.55	$908.50