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	$62.87	6.286%	$66.822	$66.82	$66.80	$66.80
Purchase #2	$221.38	9.320%	$242.0126	$242.01	$242.00	$242.00
Purchase #3	$147.44	10.138%	$162.3875	$162.39	$162.40	$162.40
Purchase #4	$90.86	4.567%	$95.0096	$95.01	$95.00	$95.00
Purchase #5	$227.94	3.485%	$235.8837	$235.88	$235.90	$235.90
Purchase #6	$123.68	11.442%	$137.8315	$137.83	$137.85	$137.80
Purchase #7	$60.75	4.784%	$63.6563	$63.66	$63.65	$63.70
7 purchase totals =	$934.92		$1,003.6032	$1,003.60	$1,003.60	$1,003.60