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	$31.78	12.274%	$35.6807	$35.68	$35.70	$35.70
Purchase #2	$121.27	9.591%	$132.901	$132.90	$132.90	$132.90
Purchase #3	$124.78	5.467%	$131.6017	$131.60	$131.60	$131.60
Purchase #4	$99.82	4.273%	$104.0853	$104.09	$104.10	$104.10
Purchase #5	$52.39	7.346%	$56.2386	$56.24	$56.25	$56.20
Purchase #6	$52.35	12.667%	$58.9812	$58.98	$59.00	$59.00
Purchase #7	$141.38	13.244%	$160.1044	$160.10	$160.10	$160.10
7 purchase totals =	$623.77		$679.5929	$679.59	$679.65	$679.60