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	$7.59	8.636%	$8.2455	$8.25	$8.25	$8.20
Purchase #2	$217.27	11.859%	$243.036	$243.04	$243.05	$243.00
Purchase #3	$11.84	6.229%	$12.5775	$12.58	$12.60	$12.60
Purchase #4	$89.80	8.501%	$97.4339	$97.43	$97.45	$97.40
Purchase #5	$137.42	10.400%	$151.7117	$151.71	$151.70	$151.70
Purchase #6	$173.40	3.213%	$178.9713	$178.97	$178.95	$179.00
Purchase #7	$100.57	10.743%	$111.3742	$111.37	$111.35	$111.40
7 purchase totals =	$737.89		$803.3501	$803.35	$803.35	$803.30