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	$36.68	9.274%	$40.0817	$40.08	$40.10	$40.10
Purchase #2	$37.50	3.567%	$38.8376	$38.84	$38.85	$38.80
Purchase #3	$92.59	3.733%	$96.0464	$96.05	$96.05	$96.00
Purchase #4	$79.87	3.351%	$82.5464	$82.55	$82.55	$82.50
Purchase #5	$6.98	7.644%	$7.5136	$7.51	$7.50	$7.50
Purchase #6	$176.25	5.178%	$185.3762	$185.38	$185.40	$185.40
Purchase #7	$103.25	5.151%	$108.5684	$108.57	$108.55	$108.60
7 purchase totals =	$533.12		$558.9703	$558.98	$559.00	$558.90