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	$14.59	13.679%	$16.5858	$16.59	$16.60	$16.60
Purchase #2	$147.83	12.179%	$165.8342	$165.83	$165.85	$165.80
Purchase #3	$45.61	10.287%	$50.3019	$50.30	$50.30	$50.30
Purchase #4	$9.99	10.342%	$11.0232	$11.02	$11.00	$11.00
Purchase #5	$169.60	10.394%	$187.2282	$187.23	$187.25	$187.20
Purchase #6	$237.86	5.743%	$251.5203	$251.52	$251.50	$251.50
Purchase #7	$130.83	5.204%	$137.6384	$137.64	$137.65	$137.60
7 purchase totals =	$756.31		$820.1320	$820.13	$820.15	$820.00