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	$103.43	13.168%	$117.0497	$117.05	$117.05	$117.00
Purchase #2	$110.93	5.387%	$116.9058	$116.91	$116.90	$116.90
Purchase #3	$92.75	10.285%	$102.2893	$102.29	$102.30	$102.30
Purchase #4	$154.82	10.820%	$171.5715	$171.57	$171.55	$171.60
Purchase #5	$97.30	11.737%	$108.7201	$108.72	$108.70	$108.70
Purchase #6	$65.57	10.551%	$72.4883	$72.49	$72.50	$72.50
Purchase #7	$15.63	6.185%	$16.5967	$16.60	$16.60	$16.60
7 purchase totals =	$640.43		$705.6214	$705.63	$705.60	$705.60