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	$15.60	13.310%	$17.6764	$17.68	$17.70	$17.70
Purchase #2	$151.64	13.792%	$172.5542	$172.55	$172.55	$172.60
Purchase #3	$48.35	12.763%	$54.5209	$54.52	$54.50	$54.50
Purchase #4	$42.28	3.685%	$43.838	$43.84	$43.85	$43.80
Purchase #5	$178.53	6.320%	$189.8131	$189.81	$189.80	$189.80
Purchase #6	$98.97	6.371%	$105.2754	$105.28	$105.30	$105.30
Purchase #7	$129.97	4.761%	$136.1579	$136.16	$136.15	$136.20
7 purchase totals =	$665.34		$719.8359	$719.84	$719.85	$719.90