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	$189.60	8.327%	$205.388	$205.39	$205.40	$205.40
Purchase #2	$70.74	10.774%	$78.3615	$78.36	$78.35	$78.40
Purchase #3	$205.30	12.323%	$230.5991	$230.60	$230.60	$230.60
Purchase #4	$128.78	3.629%	$133.4534	$133.45	$133.45	$133.50
Purchase #5	$65.72	10.147%	$72.3886	$72.39	$72.40	$72.40
Purchase #6	$36.45	9.263%	$39.8264	$39.83	$39.85	$39.80
Purchase #7	$142.38	6.434%	$151.5407	$151.54	$151.55	$151.50
7 purchase totals =	$838.97		$911.5577	$911.56	$911.60	$911.60