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	$132.95	8.700%	$144.5167	$144.52	$144.50	$144.50
Purchase #2	$233.78	3.856%	$242.7946	$242.79	$242.80	$242.80
Purchase #3	$92.50	8.590%	$100.4458	$100.45	$100.45	$100.40
Purchase #4	$229.66	5.180%	$241.5564	$241.56	$241.55	$241.60
Purchase #5	$239.78	7.557%	$257.9002	$257.90	$257.90	$257.90
Purchase #6	$145.55	10.498%	$160.8298	$160.83	$160.85	$160.80
Purchase #7	$155.76	12.208%	$174.7752	$174.78	$174.80	$174.80
7 purchase totals =	$1,229.98		$1,322.8187	$1,322.83	$1,322.85	$1,322.80