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	$24.65	11.598%	$27.5089	$27.51	$27.50	$27.50
Purchase #2	$248.45	13.751%	$282.6144	$282.61	$282.60	$282.60
Purchase #3	$21.86	5.128%	$22.981	$22.98	$23.00	$23.00
Purchase #4	$105.40	7.547%	$113.3545	$113.35	$113.35	$113.40
Purchase #5	$51.35	12.309%	$57.6707	$57.67	$57.65	$57.70
Purchase #6	$92.78	7.260%	$99.5158	$99.52	$99.50	$99.50
Purchase #7	$111.75	13.519%	$126.8575	$126.86	$126.85	$126.90
7 purchase totals =	$656.24		$730.5028	$730.50	$730.45	$730.60