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	$35.28	10.545%	$39.0003	$39.00	$39.00	$39.00
Purchase #2	$114.37	11.631%	$127.6724	$127.67	$127.65	$127.70
Purchase #3	$17.78	4.355%	$18.5543	$18.55	$18.55	$18.60
Purchase #4	$24.31	11.447%	$27.0928	$27.09	$27.10	$27.10
Purchase #5	$54.93	10.474%	$60.6834	$60.68	$60.70	$60.70
Purchase #6	$199.81	4.444%	$208.6896	$208.69	$208.70	$208.70
Purchase #7	$116.85	5.863%	$123.7009	$123.70	$123.70	$123.70
7 purchase totals =	$563.33		$605.3937	$605.38	$605.40	$605.50