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	$79.91	6.667%	$85.2376	$85.24	$85.25	$85.20
Purchase #2	$140.64	10.540%	$155.4635	$155.46	$155.45	$155.50
Purchase #3	$96.79	4.820%	$101.4553	$101.46	$101.45	$101.50
Purchase #4	$206.61	12.181%	$231.7772	$231.78	$231.80	$231.80
Purchase #5	$138.46	13.296%	$156.8696	$156.87	$156.85	$156.90
Purchase #6	$163.59	7.139%	$175.2687	$175.27	$175.25	$175.30
Purchase #7	$58.61	8.487%	$63.5842	$63.58	$63.60	$63.60
7 purchase totals =	$884.61		$969.6561	$969.66	$969.65	$969.80