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	$203.76	12.698%	$229.6334	$229.63	$229.65	$229.60
Purchase #2	$174.30	10.435%	$192.4882	$192.49	$192.50	$192.50
Purchase #3	$232.58	8.427%	$252.1795	$252.18	$252.20	$252.20
Purchase #4	$105.29	6.287%	$111.9096	$111.91	$111.90	$111.90
Purchase #5	$180.48	5.571%	$190.5345	$190.53	$190.55	$190.50
Purchase #6	$11.56	7.131%	$12.3843	$12.38	$12.40	$12.40
Purchase #7	$87.39	5.149%	$91.8897	$91.89	$91.90	$91.90
7 purchase totals =	$995.36		$1,081.0192	$1,081.01	$1,081.10	$1,081.00