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	$242.41	8.321%	$262.5809	$262.58	$262.60	$262.60
Purchase #2	$129.49	8.827%	$140.9201	$140.92	$140.90	$140.90
Purchase #3	$64.86	4.128%	$67.5374	$67.54	$67.55	$67.50
Purchase #4	$109.95	6.520%	$117.1187	$117.12	$117.10	$117.10
Purchase #5	$113.59	12.800%	$128.1295	$128.13	$128.15	$128.10
Purchase #6	$66.34	8.813%	$72.1865	$72.19	$72.20	$72.20
Purchase #7	$15.42	3.209%	$15.9148	$15.91	$15.90	$15.90
7 purchase totals =	$742.06		$804.3879	$804.39	$804.40	$804.30