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	$111.33	4.594%	$116.4445	$116.44	$116.45	$116.40
Purchase #2	$241.60	3.280%	$249.5245	$249.52	$249.50	$249.50
Purchase #3	$61.76	3.345%	$63.8259	$63.83	$63.85	$63.80
Purchase #4	$131.80	10.563%	$145.722	$145.72	$145.70	$145.70
Purchase #5	$67.28	7.635%	$72.4168	$72.42	$72.40	$72.40
Purchase #6	$117.46	12.591%	$132.2494	$132.25	$132.25	$132.20
Purchase #7	$109.54	9.260%	$119.6834	$119.68	$119.70	$119.70
7 purchase totals =	$840.77		$899.8665	$899.86	$899.85	$899.70