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	$52.98	12.104%	$59.3927	$59.39	$59.40	$59.40
Purchase #2	$166.86	5.221%	$175.5718	$175.57	$175.55	$175.60
Purchase #3	$232.69	8.429%	$252.3034	$252.30	$252.30	$252.30
Purchase #4	$52.60	4.795%	$55.1222	$55.12	$55.10	$55.10
Purchase #5	$34.30	7.233%	$36.7809	$36.78	$36.80	$36.80
Purchase #6	$157.66	13.221%	$178.5042	$178.50	$178.50	$178.50
Purchase #7	$151.76	4.264%	$158.231	$158.23	$158.25	$158.20
7 purchase totals =	$848.85		$915.9062	$915.89	$915.90	$915.90