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	$58.30	10.737%	$64.5597	$64.56	$64.55	$64.60
Purchase #2	$136.58	13.123%	$154.5034	$154.50	$154.50	$154.50
Purchase #3	$12.81	7.579%	$13.7809	$13.78	$13.80	$13.80
Purchase #4	$99.71	8.829%	$108.5134	$108.51	$108.50	$108.50
Purchase #5	$137.40	13.238%	$155.589	$155.59	$155.60	$155.60
Purchase #6	$143.49	6.458%	$152.7566	$152.76	$152.75	$152.80
Purchase #7	$88.74	3.765%	$92.0811	$92.08	$92.10	$92.10
7 purchase totals =	$677.03		$741.7841	$741.78	$741.80	$741.90