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	$235.55	8.183%	$254.8251	$254.83	$254.85	$254.80
Purchase #2	$156.93	9.766%	$172.2558	$172.26	$172.25	$172.30
Purchase #3	$161.91	6.469%	$172.384	$172.38	$172.40	$172.40
Purchase #4	$120.54	4.658%	$126.1548	$126.15	$126.15	$126.20
Purchase #5	$128.87	10.635%	$142.5753	$142.58	$142.60	$142.60
Purchase #6	$164.41	6.376%	$174.8928	$174.89	$174.90	$174.90
Purchase #7	$51.26	10.844%	$56.8186	$56.82	$56.80	$56.80
7 purchase totals =	$1,019.47		$1,099.9064	$1,099.91	$1,099.95	$1,100.00