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	$32.62	13.546%	$37.0387	$37.04	$37.05	$37.00
Purchase #2	$192.34	3.715%	$199.4854	$199.49	$199.50	$199.50
Purchase #3	$135.84	13.798%	$154.5832	$154.58	$154.60	$154.60
Purchase #4	$46.54	12.392%	$52.3072	$52.31	$52.30	$52.30
Purchase #5	$137.77	5.563%	$145.4341	$145.43	$145.45	$145.40
Purchase #6	$53.59	7.370%	$57.5396	$57.54	$57.55	$57.50
Purchase #7	$30.64	12.505%	$34.4715	$34.47	$34.45	$34.50
7 purchase totals =	$629.34		$680.8597	$680.86	$680.90	$680.80