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	$233.75	11.182%	$259.8879	$259.89	$259.90	$259.90
Purchase #2	$54.76	10.685%	$60.6111	$60.61	$60.60	$60.60
Purchase #3	$140.37	13.833%	$159.7874	$159.79	$159.80	$159.80
Purchase #4	$126.78	12.724%	$142.9115	$142.91	$142.90	$142.90
Purchase #5	$39.53	13.487%	$44.8614	$44.86	$44.85	$44.90
Purchase #6	$239.40	8.762%	$260.3762	$260.38	$260.40	$260.40
Purchase #7	$60.37	9.806%	$66.2899	$66.29	$66.30	$66.30
7 purchase totals =	$894.96		$994.7254	$994.73	$994.75	$994.80