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	$27.38	5.457%	$28.8741	$28.87	$28.85	$28.90
Purchase #2	$223.77	11.195%	$248.8211	$248.82	$248.80	$248.80
Purchase #3	$51.92	8.638%	$56.4048	$56.40	$56.40	$56.40
Purchase #4	$77.39	10.847%	$85.7845	$85.78	$85.80	$85.80
Purchase #5	$131.97	9.631%	$144.68	$144.68	$144.70	$144.70
Purchase #6	$124.52	5.443%	$131.2976	$131.30	$131.30	$131.30
Purchase #7	$117.52	8.104%	$127.0438	$127.04	$127.05	$127.00
7 purchase totals =	$754.47		$822.9059	$822.89	$822.90	$822.90