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	$116.93	5.788%	$123.6979	$123.70	$123.70	$123.70
Purchase #2	$68.45	4.178%	$71.3098	$71.31	$71.30	$71.30
Purchase #3	$167.85	11.802%	$187.6597	$187.66	$187.65	$187.70
Purchase #4	$124.66	4.323%	$130.0491	$130.05	$130.05	$130.00
Purchase #5	$239.60	4.104%	$249.4332	$249.43	$249.45	$249.40
Purchase #6	$105.28	3.715%	$109.1912	$109.19	$109.20	$109.20
Purchase #7	$190.27	7.488%	$204.5174	$204.52	$204.50	$204.50
7 purchase totals =	$1,013.04		$1,075.8583	$1,075.86	$1,075.85	$1,075.80