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	$74.49	13.554%	$84.5864	$84.59	$84.60	$84.60
Purchase #2	$114.72	10.789%	$127.0971	$127.10	$127.10	$127.10
Purchase #3	$226.47	12.814%	$255.4899	$255.49	$255.50	$255.50
Purchase #4	$99.99	9.614%	$109.603	$109.60	$109.60	$109.60
Purchase #5	$85.38	3.105%	$88.031	$88.03	$88.05	$88.00
Purchase #6	$135.87	12.265%	$152.5345	$152.53	$152.55	$152.50
Purchase #7	$175.84	7.663%	$189.3146	$189.31	$189.30	$189.30
7 purchase totals =	$912.76		$1,006.6565	$1,006.65	$1,006.70	$1,006.60