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	$137.35	13.195%	$155.4733	$155.47	$155.45	$155.50
Purchase #2	$183.51	12.792%	$206.9846	$206.98	$207.00	$207.00
Purchase #3	$227.60	3.642%	$235.8892	$235.89	$235.90	$235.90
Purchase #4	$244.77	9.624%	$268.3267	$268.33	$268.35	$268.30
Purchase #5	$96.76	13.505%	$109.8274	$109.83	$109.85	$109.80
Purchase #6	$112.31	4.745%	$117.6391	$117.64	$117.65	$117.60
Purchase #7	$94.45	11.662%	$105.4648	$105.46	$105.45	$105.50
7 purchase totals =	$1,096.75		$1,199.6051	$1,199.60	$1,199.65	$1,199.60