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	$16.67	5.707%	$17.6214	$17.62	$17.60	$17.60
Purchase #2	$178.37	3.689%	$184.9501	$184.95	$184.95	$185.00
Purchase #3	$154.73	7.557%	$166.4229	$166.42	$166.40	$166.40
Purchase #4	$103.57	10.472%	$114.4159	$114.42	$114.40	$114.40
Purchase #5	$213.34	4.403%	$222.7334	$222.73	$222.75	$222.70
Purchase #6	$116.39	7.522%	$125.1449	$125.14	$125.15	$125.10
Purchase #7	$103.99	7.240%	$111.5189	$111.52	$111.50	$111.50
7 purchase totals =	$887.06		$942.8075	$942.80	$942.75	$942.70