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	$17.80	3.674%	$18.454	$18.45	$18.45	$18.50
Purchase #2	$56.38	4.652%	$59.0028	$59.00	$59.00	$59.00
Purchase #3	$204.71	4.768%	$214.4706	$214.47	$214.45	$214.50
Purchase #4	$210.40	7.655%	$226.5061	$226.51	$226.50	$226.50
Purchase #5	$164.85	5.381%	$173.7206	$173.72	$173.70	$173.70
Purchase #6	$156.94	5.323%	$165.2939	$165.29	$165.30	$165.30
Purchase #7	$48.64	11.167%	$54.0716	$54.07	$54.05	$54.10
7 purchase totals =	$859.72		$911.5196	$911.51	$911.45	$911.60