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	$12.29	4.606%	$12.8561	$12.86	$12.85	$12.90
Purchase #2	$50.94	4.420%	$53.1915	$53.19	$53.20	$53.20
Purchase #3	$133.96	6.318%	$142.4236	$142.42	$142.40	$142.40
Purchase #4	$136.70	13.834%	$155.6111	$155.61	$155.60	$155.60
Purchase #5	$217.67	10.407%	$240.3229	$240.32	$240.30	$240.30
Purchase #6	$111.43	6.784%	$118.9894	$118.99	$119.00	$119.00
Purchase #7	$190.67	10.105%	$209.9372	$209.94	$209.95	$209.90
7 purchase totals =	$853.66		$933.3318	$933.33	$933.30	$933.30