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	$16.60	7.624%	$17.8656	$17.87	$17.85	$17.90
Purchase #2	$72.48	4.312%	$75.6053	$75.61	$75.60	$75.60
Purchase #3	$143.60	13.175%	$162.5193	$162.52	$162.50	$162.50
Purchase #4	$177.74	5.431%	$187.3931	$187.39	$187.40	$187.40
Purchase #5	$119.45	10.251%	$131.6948	$131.69	$131.70	$131.70
Purchase #6	$108.60	3.151%	$112.022	$112.02	$112.00	$112.00
Purchase #7	$121.54	4.610%	$127.143	$127.14	$127.15	$127.10
7 purchase totals =	$760.01		$814.2431	$814.24	$814.20	$814.20