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	$63.27	7.261%	$67.864	$67.86	$67.85	$67.90
Purchase #2	$27.54	5.388%	$29.0239	$29.02	$29.00	$29.00
Purchase #3	$154.86	12.472%	$174.1741	$174.17	$174.15	$174.20
Purchase #4	$145.85	13.492%	$165.5281	$165.53	$165.55	$165.50
Purchase #5	$132.67	8.440%	$143.8673	$143.87	$143.85	$143.90
Purchase #6	$98.90	6.782%	$105.6074	$105.61	$105.60	$105.60
Purchase #7	$40.79	5.433%	$43.0061	$43.01	$43.00	$43.00
7 purchase totals =	$663.88		$729.0709	$729.07	$729.00	$729.10