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	$72.60	10.743%	$80.3994	$80.40	$80.40	$80.40
Purchase #2	$85.77	10.140%	$94.4671	$94.47	$94.45	$94.50
Purchase #3	$15.70	7.164%	$16.8247	$16.82	$16.80	$16.80
Purchase #4	$102.97	13.553%	$116.9255	$116.93	$116.95	$116.90
Purchase #5	$233.42	3.730%	$242.1266	$242.13	$242.15	$242.10
Purchase #6	$171.69	10.834%	$190.2909	$190.29	$190.30	$190.30
Purchase #7	$41.35	12.165%	$46.3802	$46.38	$46.40	$46.40
7 purchase totals =	$723.50		$787.4144	$787.42	$787.45	$787.40