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	$95.33	5.500%	$100.5732	$100.57	$100.55	$100.60
Purchase #2	$163.61	10.292%	$180.4487	$180.45	$180.45	$180.40
Purchase #3	$97.84	6.139%	$103.8464	$103.85	$103.85	$103.80
Purchase #4	$16.99	8.496%	$18.4335	$18.43	$18.45	$18.40
Purchase #5	$203.46	13.144%	$230.2028	$230.20	$230.20	$230.20
Purchase #6	$37.57	13.182%	$42.5225	$42.52	$42.50	$42.50
Purchase #7	$141.53	11.277%	$157.4903	$157.49	$157.50	$157.50
7 purchase totals =	$756.33		$833.5174	$833.51	$833.50	$833.40