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	$15.92	6.341%	$16.9295	$16.93	$16.95	$16.90
Purchase #2	$134.25	4.564%	$140.3772	$140.38	$140.40	$140.40
Purchase #3	$9.57	7.870%	$10.3232	$10.32	$10.30	$10.30
Purchase #4	$43.31	6.777%	$46.2451	$46.25	$46.25	$46.20
Purchase #5	$177.82	12.538%	$200.1151	$200.12	$200.10	$200.10
Purchase #6	$51.85	8.594%	$56.306	$56.31	$56.30	$56.30
Purchase #7	$58.89	4.581%	$61.5878	$61.59	$61.60	$61.60
7 purchase totals =	$491.61		$531.8839	$531.90	$531.90	$531.80