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	$228.78	13.390%	$259.4136	$259.41	$259.40	$259.40
Purchase #2	$95.83	9.594%	$105.0239	$105.02	$105.00	$105.00
Purchase #3	$35.66	10.631%	$39.451	$39.45	$39.45	$39.50
Purchase #4	$79.70	13.748%	$90.6572	$90.66	$90.65	$90.70
Purchase #5	$96.35	8.795%	$104.824	$104.82	$104.80	$104.80
Purchase #6	$75.41	9.311%	$82.4314	$82.43	$82.45	$82.40
Purchase #7	$40.76	13.288%	$46.1762	$46.18	$46.20	$46.20
7 purchase totals =	$652.49		$727.9773	$727.97	$727.95	$728.00