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	$81.96	10.445%	$90.5207	$90.52	$90.50	$90.50
Purchase #2	$20.61	4.141%	$21.4635	$21.46	$21.45	$21.50
Purchase #3	$239.64	9.800%	$263.1247	$263.12	$263.10	$263.10
Purchase #4	$89.84	3.550%	$93.0293	$93.03	$93.05	$93.00
Purchase #5	$100.94	12.447%	$113.504	$113.50	$113.50	$113.50
Purchase #6	$141.91	9.662%	$155.6213	$155.62	$155.60	$155.60
Purchase #7	$37.81	8.711%	$41.1036	$41.10	$41.10	$41.10
7 purchase totals =	$712.71		$778.3671	$778.35	$778.30	$778.30