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	$104.76	3.649%	$108.5827	$108.58	$108.60	$108.60
Purchase #2	$107.29	5.232%	$112.9034	$112.90	$112.90	$112.90
Purchase #3	$100.89	10.404%	$111.3866	$111.39	$111.40	$111.40
Purchase #4	$114.32	4.145%	$119.0586	$119.06	$119.05	$119.10
Purchase #5	$31.29	4.252%	$32.6205	$32.62	$32.60	$32.60
Purchase #6	$196.38	9.188%	$214.4234	$214.42	$214.40	$214.40
Purchase #7	$184.86	4.637%	$193.432	$193.43	$193.45	$193.40
7 purchase totals =	$839.79		$892.4072	$892.40	$892.40	$892.40