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	$144.74	12.308%	$162.5546	$162.55	$162.55	$162.60
Purchase #2	$81.73	9.608%	$89.5826	$89.58	$89.60	$89.60
Purchase #3	$127.49	9.599%	$139.7278	$139.73	$139.75	$139.70
Purchase #4	$168.64	9.496%	$184.6541	$184.65	$184.65	$184.70
Purchase #5	$146.97	5.649%	$155.2723	$155.27	$155.25	$155.30
Purchase #6	$134.91	6.291%	$143.3972	$143.40	$143.40	$143.40
Purchase #7	$38.70	11.176%	$43.0251	$43.03	$43.05	$43.00
7 purchase totals =	$843.18		$918.2137	$918.21	$918.25	$918.30