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	$245.51	13.367%	$278.3273	$278.33	$278.35	$278.30
Purchase #2	$126.32	6.324%	$134.3085	$134.31	$134.30	$134.30
Purchase #3	$219.39	8.864%	$238.8367	$238.84	$238.85	$238.80
Purchase #4	$128.74	10.648%	$142.4482	$142.45	$142.45	$142.40
Purchase #5	$194.99	10.660%	$215.7759	$215.78	$215.80	$215.80
Purchase #6	$213.95	4.274%	$223.0942	$223.09	$223.10	$223.10
Purchase #7	$79.99	3.285%	$82.6177	$82.62	$82.60	$82.60
7 purchase totals =	$1,208.89		$1,315.4085	$1,315.42	$1,315.45	$1,315.30