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	$115.47	9.451%	$126.3831	$126.38	$126.40	$126.40
Purchase #2	$150.84	13.744%	$171.5714	$171.57	$171.55	$171.60
Purchase #3	$46.71	4.729%	$48.9189	$48.92	$48.90	$48.90
Purchase #4	$214.96	10.181%	$236.8451	$236.85	$236.85	$236.80
Purchase #5	$95.72	5.301%	$100.7941	$100.79	$100.80	$100.80
Purchase #6	$56.55	3.483%	$58.5196	$58.52	$58.50	$58.50
Purchase #7	$52.71	3.565%	$54.5891	$54.59	$54.60	$54.60
7 purchase totals =	$732.96		$797.6213	$797.62	$797.60	$797.60