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	$63.88	12.869%	$72.1007	$72.10	$72.10	$72.10
Purchase #2	$138.78	8.427%	$150.475	$150.48	$150.50	$150.50
Purchase #3	$99.78	4.273%	$104.0436	$104.04	$104.05	$104.00
Purchase #4	$99.50	8.771%	$108.2271	$108.23	$108.25	$108.20
Purchase #5	$17.92	12.103%	$20.0889	$20.09	$20.10	$20.10
Purchase #6	$63.69	4.590%	$66.6134	$66.61	$66.60	$66.60
Purchase #7	$84.91	9.491%	$92.9688	$92.97	$92.95	$93.00
7 purchase totals =	$568.46		$614.5175	$614.52	$614.55	$614.50