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	$244.76	5.394%	$257.9624	$257.96	$257.95	$258.00
Purchase #2	$53.87	10.228%	$59.3798	$59.38	$59.40	$59.40
Purchase #3	$26.63	8.499%	$28.8933	$28.89	$28.90	$28.90
Purchase #4	$143.58	12.105%	$160.9604	$160.96	$160.95	$161.00
Purchase #5	$111.43	13.332%	$126.2858	$126.29	$126.30	$126.30
Purchase #6	$154.89	8.335%	$167.8001	$167.80	$167.80	$167.80
Purchase #7	$80.51	11.324%	$89.627	$89.63	$89.65	$89.60
7 purchase totals =	$815.67		$890.9088	$890.91	$890.95	$891.00