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	$93.26	6.784%	$99.5868	$99.59	$99.60	$99.60
Purchase #2	$26.68	10.864%	$29.5785	$29.58	$29.60	$29.60
Purchase #3	$146.25	3.407%	$151.2327	$151.23	$151.25	$151.20
Purchase #4	$19.77	9.833%	$21.714	$21.71	$21.70	$21.70
Purchase #5	$98.48	13.311%	$111.5887	$111.59	$111.60	$111.60
Purchase #6	$166.67	11.639%	$186.0687	$186.07	$186.05	$186.10
Purchase #7	$93.88	10.579%	$103.8116	$103.81	$103.80	$103.80
7 purchase totals =	$644.99		$703.5810	$703.58	$703.60	$703.60