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	$113.50	8.378%	$123.009	$123.01	$123.00	$123.00
Purchase #2	$196.70	13.128%	$222.5228	$222.52	$222.50	$222.50
Purchase #3	$9.52	10.644%	$10.5333	$10.53	$10.55	$10.50
Purchase #4	$77.29	9.628%	$84.7315	$84.73	$84.75	$84.70
Purchase #5	$100.98	7.212%	$108.2627	$108.26	$108.25	$108.30
Purchase #6	$102.81	8.495%	$111.5437	$111.54	$111.55	$111.50
Purchase #7	$187.70	5.152%	$197.3703	$197.37	$197.35	$197.40
7 purchase totals =	$788.50		$857.9733	$857.96	$857.95	$857.90