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	$108.71	10.780%	$120.4289	$120.43	$120.45	$120.40
Purchase #2	$247.96	5.105%	$260.6184	$260.62	$260.60	$260.60
Purchase #3	$184.79	8.685%	$200.839	$200.84	$200.85	$200.80
Purchase #4	$73.31	7.466%	$78.7833	$78.78	$78.80	$78.80
Purchase #5	$70.37	3.656%	$72.9427	$72.94	$72.95	$72.90
Purchase #6	$137.34	9.493%	$150.3777	$150.38	$150.40	$150.40
Purchase #7	$6.55	6.162%	$6.9536	$6.95	$6.95	$7.00
7 purchase totals =	$829.03		$890.9436	$890.94	$891.00	$890.90