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	$109.38	6.536%	$116.5291	$116.53	$116.55	$116.50
Purchase #2	$239.59	8.472%	$259.8881	$259.89	$259.90	$259.90
Purchase #3	$166.52	5.412%	$175.5321	$175.53	$175.55	$175.50
Purchase #4	$61.62	7.772%	$66.4091	$66.41	$66.40	$66.40
Purchase #5	$173.58	8.212%	$187.8344	$187.83	$187.85	$187.80
Purchase #6	$32.61	5.592%	$34.4336	$34.43	$34.45	$34.40
Purchase #7	$87.65	13.353%	$99.3539	$99.35	$99.35	$99.40
7 purchase totals =	$870.95		$939.9803	$939.97	$940.05	$939.90