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	$12.50	10.382%	$13.7978	$13.80	$13.80	$13.80
Purchase #2	$39.39	10.366%	$43.4732	$43.47	$43.45	$43.50
Purchase #3	$174.27	6.141%	$184.9719	$184.97	$184.95	$185.00
Purchase #4	$138.35	6.818%	$147.7827	$147.78	$147.80	$147.80
Purchase #5	$51.72	11.458%	$57.6461	$57.65	$57.65	$57.60
Purchase #6	$75.72	3.673%	$78.5012	$78.50	$78.50	$78.50
Purchase #7	$216.77	10.537%	$239.6111	$239.61	$239.60	$239.60
7 purchase totals =	$708.72		$765.7840	$765.78	$765.75	$765.80