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	$79.76	13.591%	$90.6002	$90.60	$90.60	$90.60
Purchase #2	$248.94	5.451%	$262.5097	$262.51	$262.50	$262.50
Purchase #3	$161.80	8.538%	$175.6145	$175.61	$175.60	$175.60
Purchase #4	$238.42	6.771%	$254.5634	$254.56	$254.55	$254.60
Purchase #5	$53.66	8.795%	$58.3794	$58.38	$58.40	$58.40
Purchase #6	$159.55	11.622%	$178.0929	$178.09	$178.10	$178.10
Purchase #7	$118.79	4.250%	$123.8386	$123.84	$123.85	$123.80
7 purchase totals =	$1,060.92		$1,143.5987	$1,143.59	$1,143.60	$1,143.60