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	$57.94	12.794%	$65.3528	$65.35	$65.35	$65.40
Purchase #2	$116.57	3.212%	$120.3142	$120.31	$120.30	$120.30
Purchase #3	$209.67	3.573%	$217.1615	$217.16	$217.15	$217.20
Purchase #4	$167.60	10.727%	$185.5785	$185.58	$185.60	$185.60
Purchase #5	$117.25	3.685%	$121.5707	$121.57	$121.55	$121.60
Purchase #6	$13.72	10.233%	$15.124	$15.12	$15.10	$15.10
Purchase #7	$83.52	7.512%	$89.794	$89.79	$89.80	$89.80
7 purchase totals =	$766.27		$814.8957	$814.88	$814.85	$815.00