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	$57.91	13.677%	$65.8304	$65.83	$65.85	$65.80
Purchase #2	$166.76	3.447%	$172.5082	$172.51	$172.50	$172.50
Purchase #3	$89.49	10.539%	$98.9214	$98.92	$98.90	$98.90
Purchase #4	$78.64	13.582%	$89.3209	$89.32	$89.30	$89.30
Purchase #5	$187.59	3.292%	$193.7655	$193.77	$193.75	$193.80
Purchase #6	$110.85	13.378%	$125.6795	$125.68	$125.70	$125.70
Purchase #7	$50.38	12.322%	$56.5878	$56.59	$56.60	$56.60
7 purchase totals =	$741.62		$802.6137	$802.62	$802.60	$802.60