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	$129.80	7.798%	$139.9218	$139.92	$139.90	$139.90
Purchase #2	$115.63	13.694%	$131.4644	$131.46	$131.45	$131.50
Purchase #3	$206.29	11.555%	$230.1268	$230.13	$230.15	$230.10
Purchase #4	$163.51	7.176%	$175.2435	$175.24	$175.25	$175.20
Purchase #5	$49.42	12.803%	$55.7472	$55.75	$55.75	$55.70
Purchase #6	$137.36	10.678%	$152.0273	$152.03	$152.05	$152.00
Purchase #7	$117.72	12.210%	$132.0936	$132.09	$132.10	$132.10
7 purchase totals =	$919.73		$1,016.6246	$1,016.62	$1,016.65	$1,016.50