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	$59.52	11.347%	$66.2737	$66.27	$66.25	$66.30
Purchase #2	$107.60	3.596%	$111.4693	$111.47	$111.45	$111.50
Purchase #3	$24.94	3.524%	$25.8189	$25.82	$25.80	$25.80
Purchase #4	$90.61	12.394%	$101.8402	$101.84	$101.85	$101.80
Purchase #5	$114.86	5.149%	$120.7741	$120.77	$120.75	$120.80
Purchase #6	$151.34	4.653%	$158.3819	$158.38	$158.40	$158.40
Purchase #7	$210.77	8.696%	$229.0986	$229.10	$229.10	$229.10
7 purchase totals =	$759.64		$813.6567	$813.65	$813.60	$813.70