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	$51.83	5.742%	$54.8061	$54.81	$54.80	$54.80
Purchase #2	$91.93	8.558%	$99.7974	$99.80	$99.80	$99.80
Purchase #3	$93.67	6.103%	$99.3867	$99.39	$99.40	$99.40
Purchase #4	$93.37	7.134%	$100.031	$100.03	$100.05	$100.00
Purchase #5	$69.68	5.592%	$73.5765	$73.58	$73.60	$73.60
Purchase #6	$241.71	10.671%	$267.5029	$267.50	$267.50	$267.50
Purchase #7	$100.44	5.351%	$105.8145	$105.81	$105.80	$105.80
7 purchase totals =	$742.63		$800.9151	$800.92	$800.95	$800.90