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	$42.94	12.626%	$48.3616	$48.36	$48.35	$48.40
Purchase #2	$59.60	5.286%	$62.7505	$62.75	$62.75	$62.80
Purchase #3	$107.58	3.116%	$110.9322	$110.93	$110.95	$110.90
Purchase #4	$60.97	9.798%	$66.9438	$66.94	$66.95	$66.90
Purchase #5	$158.87	3.570%	$164.5417	$164.54	$164.55	$164.50
Purchase #6	$114.56	11.223%	$127.4171	$127.42	$127.40	$127.40
Purchase #7	$177.39	12.249%	$199.1185	$199.12	$199.10	$199.10
7 purchase totals =	$721.91		$780.0654	$780.06	$780.05	$780.00