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	$142.35	9.393%	$155.7209	$155.72	$155.70	$155.70
Purchase #2	$111.47	5.186%	$117.2508	$117.25	$117.25	$117.30
Purchase #3	$39.59	12.286%	$44.454	$44.45	$44.45	$44.50
Purchase #4	$221.31	4.671%	$231.6474	$231.65	$231.65	$231.60
Purchase #5	$132.78	9.450%	$145.3277	$145.33	$145.35	$145.30
Purchase #6	$169.91	7.615%	$182.8486	$182.85	$182.85	$182.80
Purchase #7	$186.76	12.765%	$210.5999	$210.60	$210.60	$210.60
7 purchase totals =	$1,004.17		$1,087.8493	$1,087.85	$1,087.85	$1,087.80