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	$24.60	12.127%	$27.5832	$27.58	$27.60	$27.60
Purchase #2	$245.93	6.568%	$262.0827	$262.08	$262.10	$262.10
Purchase #3	$53.63	11.187%	$59.6296	$59.63	$59.65	$59.60
Purchase #4	$9.30	13.745%	$10.5783	$10.58	$10.60	$10.60
Purchase #5	$56.77	8.129%	$61.3848	$61.38	$61.40	$61.40
Purchase #6	$68.36	5.398%	$72.0501	$72.05	$72.05	$72.10
Purchase #7	$144.97	6.286%	$154.0828	$154.08	$154.10	$154.10
7 purchase totals =	$603.56		$647.3915	$647.38	$647.50	$647.50