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	$52.94	6.511%	$56.3869	$56.39	$56.40	$56.40
Purchase #2	$214.72	10.704%	$237.7036	$237.70	$237.70	$237.70
Purchase #3	$46.50	12.422%	$52.2762	$52.28	$52.30	$52.30
Purchase #4	$27.52	12.690%	$31.0123	$31.01	$31.00	$31.00
Purchase #5	$198.34	6.145%	$210.528	$210.53	$210.55	$210.50
Purchase #6	$129.44	9.390%	$141.5944	$141.59	$141.60	$141.60
Purchase #7	$11.86	3.580%	$12.2846	$12.28	$12.30	$12.30
7 purchase totals =	$681.32		$741.7860	$741.78	$741.85	$741.80