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	$9.55	5.632%	$10.0879	$10.09	$10.10	$10.10
Purchase #2	$83.80	12.493%	$94.2691	$94.27	$94.25	$94.30
Purchase #3	$144.95	4.510%	$151.4872	$151.49	$151.50	$151.50
Purchase #4	$238.25	4.702%	$249.4525	$249.45	$249.45	$249.50
Purchase #5	$128.87	4.391%	$134.5287	$134.53	$134.55	$134.50
Purchase #6	$71.60	9.450%	$78.3662	$78.37	$78.35	$78.40
Purchase #7	$64.68	10.808%	$71.6706	$71.67	$71.65	$71.70
7 purchase totals =	$741.70		$789.8622	$789.87	$789.85	$790.00