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	$127.77	13.353%	$144.8311	$144.83	$144.85	$144.80
Purchase #2	$50.47	13.442%	$57.2542	$57.25	$57.25	$57.30
Purchase #3	$11.82	7.458%	$12.7015	$12.70	$12.70	$12.70
Purchase #4	$188.25	6.367%	$200.2359	$200.24	$200.25	$200.20
Purchase #5	$85.77	4.556%	$89.6777	$89.68	$89.70	$89.70
Purchase #6	$200.84	3.823%	$208.5181	$208.52	$208.50	$208.50
Purchase #7	$56.61	11.428%	$63.0794	$63.08	$63.10	$63.10
7 purchase totals =	$721.53		$776.2979	$776.30	$776.35	$776.30