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	$66.99	4.488%	$69.9965	$70.00	$70.00	$70.00
Purchase #2	$43.27	13.189%	$48.9769	$48.98	$49.00	$49.00
Purchase #3	$109.91	12.518%	$123.6685	$123.67	$123.65	$123.70
Purchase #4	$62.72	12.653%	$70.656	$70.66	$70.65	$70.70
Purchase #5	$215.31	10.743%	$238.4408	$238.44	$238.45	$238.40
Purchase #6	$145.89	9.595%	$159.8881	$159.89	$159.90	$159.90
Purchase #7	$160.33	11.266%	$178.3928	$178.39	$178.40	$178.40
7 purchase totals =	$804.42		$890.0196	$890.03	$890.05	$890.10