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	$9.57	11.436%	$10.6644	$10.66	$10.65	$10.70
Purchase #2	$171.76	8.509%	$186.3751	$186.38	$186.40	$186.40
Purchase #3	$32.90	12.637%	$37.0576	$37.06	$37.05	$37.10
Purchase #4	$86.42	5.804%	$91.4358	$91.44	$91.45	$91.40
Purchase #5	$134.88	4.380%	$140.7877	$140.79	$140.80	$140.80
Purchase #6	$96.65	3.292%	$99.8317	$99.83	$99.85	$99.80
Purchase #7	$175.85	9.537%	$192.6208	$192.62	$192.60	$192.60
7 purchase totals =	$708.03		$758.7731	$758.78	$758.80	$758.80