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	$193.79	12.234%	$217.4983	$217.50	$217.50	$217.50
Purchase #2	$71.95	8.536%	$78.0917	$78.09	$78.10	$78.10
Purchase #3	$79.38	7.608%	$85.4192	$85.42	$85.40	$85.40
Purchase #4	$25.96	3.518%	$26.8733	$26.87	$26.85	$26.90
Purchase #5	$76.35	7.750%	$82.2671	$82.27	$82.25	$82.30
Purchase #6	$21.47	11.188%	$23.8721	$23.87	$23.85	$23.90
Purchase #7	$146.71	4.734%	$153.6553	$153.66	$153.65	$153.70
7 purchase totals =	$615.61		$667.6770	$667.68	$667.60	$667.80