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	$8.67	13.574%	$9.8469	$9.85	$9.85	$9.80
Purchase #2	$53.45	11.671%	$59.6881	$59.69	$59.70	$59.70
Purchase #3	$202.54	13.189%	$229.253	$229.25	$229.25	$229.30
Purchase #4	$33.89	3.553%	$35.0941	$35.09	$35.10	$35.10
Purchase #5	$62.45	5.312%	$65.7673	$65.77	$65.75	$65.80
Purchase #6	$57.71	3.329%	$59.6312	$59.63	$59.65	$59.60
Purchase #7	$247.68	9.221%	$270.5186	$270.52	$270.50	$270.50
7 purchase totals =	$666.39		$729.7992	$729.80	$729.80	$729.80