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	$11.41	10.496%	$12.6076	$12.61	$12.60	$12.60
Purchase #2	$94.77	6.450%	$100.8827	$100.88	$100.90	$100.90
Purchase #3	$163.88	9.794%	$179.9304	$179.93	$179.95	$179.90
Purchase #4	$39.69	5.252%	$41.7745	$41.77	$41.75	$41.80
Purchase #5	$133.76	13.524%	$151.8497	$151.85	$151.85	$151.80
Purchase #6	$204.81	12.312%	$230.0262	$230.03	$230.05	$230.00
Purchase #7	$12.72	4.555%	$13.2994	$13.30	$13.30	$13.30
7 purchase totals =	$661.04		$730.3705	$730.37	$730.40	$730.30