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	$46.40	5.174%	$48.8007	$48.80	$48.80	$48.80
Purchase #2	$240.49	3.755%	$249.5204	$249.52	$249.50	$249.50
Purchase #3	$162.93	10.583%	$180.1729	$180.17	$180.15	$180.20
Purchase #4	$23.28	9.250%	$25.4334	$25.43	$25.45	$25.40
Purchase #5	$173.60	12.365%	$195.0656	$195.07	$195.05	$195.10
Purchase #6	$11.27	10.492%	$12.4524	$12.45	$12.45	$12.50
Purchase #7	$71.55	9.127%	$78.0804	$78.08	$78.10	$78.10
7 purchase totals =	$729.52		$789.5258	$789.52	$789.50	$789.60