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	$21.55	8.189%	$23.3147	$23.31	$23.30	$23.30
Purchase #2	$108.93	13.695%	$123.848	$123.85	$123.85	$123.80
Purchase #3	$32.25	3.333%	$33.3249	$33.32	$33.30	$33.30
Purchase #4	$13.66	10.453%	$15.0879	$15.09	$15.10	$15.10
Purchase #5	$31.52	6.631%	$33.6101	$33.61	$33.60	$33.60
Purchase #6	$33.35	3.182%	$34.4112	$34.41	$34.40	$34.40
Purchase #7	$66.74	6.792%	$71.273	$71.27	$71.25	$71.30
7 purchase totals =	$308.00		$334.8698	$334.86	$334.80	$334.80