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	$54.35	9.471%	$59.4975	$59.50	$59.50	$59.50
Purchase #2	$118.83	8.106%	$128.4624	$128.46	$128.45	$128.50
Purchase #3	$50.36	4.114%	$52.4318	$52.43	$52.45	$52.40
Purchase #4	$87.29	6.110%	$92.6234	$92.62	$92.60	$92.60
Purchase #5	$163.40	12.519%	$183.856	$183.86	$183.85	$183.90
Purchase #6	$168.51	6.516%	$179.4901	$179.49	$179.50	$179.50
Purchase #7	$86.26	5.572%	$91.0664	$91.07	$91.05	$91.10
7 purchase totals =	$729.00		$787.4276	$787.43	$787.40	$787.50