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	$19.41	8.260%	$21.0133	$21.01	$21.00	$21.00
Purchase #2	$212.28	6.464%	$226.0018	$226.00	$226.00	$226.00
Purchase #3	$202.34	3.136%	$208.6854	$208.69	$208.70	$208.70
Purchase #4	$136.78	4.784%	$143.3236	$143.32	$143.30	$143.30
Purchase #5	$137.38	4.156%	$143.0895	$143.09	$143.10	$143.10
Purchase #6	$82.75	9.506%	$90.6162	$90.62	$90.60	$90.60
Purchase #7	$207.37	10.174%	$228.4678	$228.47	$228.45	$228.50
7 purchase totals =	$998.31		$1,061.1976	$1,061.20	$1,061.15	$1,061.20