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	$62.73	8.856%	$68.2854	$68.29	$68.30	$68.30
Purchase #2	$58.78	6.462%	$62.5784	$62.58	$62.60	$62.60
Purchase #3	$157.75	5.685%	$166.7181	$166.72	$166.70	$166.70
Purchase #4	$66.28	10.168%	$73.0194	$73.02	$73.00	$73.00
Purchase #5	$104.69	4.736%	$109.6481	$109.65	$109.65	$109.60
Purchase #6	$6.99	6.544%	$7.4474	$7.45	$7.45	$7.40
Purchase #7	$140.96	7.397%	$151.3868	$151.39	$151.40	$151.40
7 purchase totals =	$598.18		$639.0836	$639.10	$639.10	$639.00