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	$120.76	6.346%	$128.4234	$128.42	$128.40	$128.40
Purchase #2	$121.54	4.756%	$127.3204	$127.32	$127.30	$127.30
Purchase #3	$134.61	9.163%	$146.9443	$146.94	$146.95	$146.90
Purchase #4	$174.85	12.104%	$196.0138	$196.01	$196.00	$196.00
Purchase #5	$215.78	3.167%	$222.6138	$222.61	$222.60	$222.60
Purchase #6	$183.61	10.486%	$202.8633	$202.86	$202.85	$202.90
Purchase #7	$239.94	9.547%	$262.8471	$262.85	$262.85	$262.80
7 purchase totals =	$1,191.09		$1,287.0261	$1,287.01	$1,286.95	$1,286.90