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	$36.86	8.379%	$39.9485	$39.95	$39.95	$39.90
Purchase #2	$185.29	5.172%	$194.8732	$194.87	$194.85	$194.90
Purchase #3	$13.82	11.852%	$15.4579	$15.46	$15.45	$15.50
Purchase #4	$42.76	12.237%	$47.9925	$47.99	$48.00	$48.00
Purchase #5	$96.92	9.187%	$105.824	$105.82	$105.80	$105.80
Purchase #6	$23.97	7.190%	$25.6934	$25.69	$25.70	$25.70
Purchase #7	$143.72	12.774%	$162.0788	$162.08	$162.10	$162.10
7 purchase totals =	$543.34		$591.8683	$591.86	$591.85	$591.90