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	$18.45	10.723%	$20.4284	$20.43	$20.45	$20.40
Purchase #2	$244.87	3.698%	$253.9253	$253.93	$253.95	$253.90
Purchase #3	$82.98	11.436%	$92.4696	$92.47	$92.45	$92.50
Purchase #4	$82.25	5.126%	$86.4661	$86.47	$86.45	$86.50
Purchase #5	$157.57	10.250%	$173.7209	$173.72	$173.70	$173.70
Purchase #6	$160.91	9.230%	$175.762	$175.76	$175.75	$175.80
Purchase #7	$40.80	6.502%	$43.4528	$43.45	$43.45	$43.50
7 purchase totals =	$787.83		$846.2251	$846.23	$846.20	$846.30