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	$225.63	13.856%	$256.8933	$256.89	$256.90	$256.90
Purchase #2	$60.73	5.539%	$64.0938	$64.09	$64.10	$64.10
Purchase #3	$170.71	11.832%	$190.9084	$190.91	$190.90	$190.90
Purchase #4	$128.72	13.463%	$146.0496	$146.05	$146.05	$146.00
Purchase #5	$144.75	4.342%	$151.035	$151.04	$151.05	$151.00
Purchase #6	$19.84	6.223%	$21.0746	$21.07	$21.05	$21.10
Purchase #7	$157.85	10.772%	$174.8536	$174.85	$174.85	$174.90
7 purchase totals =	$908.23		$1,004.9083	$1,004.90	$1,004.90	$1,004.90