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	$96.27	13.320%	$109.0932	$109.09	$109.10	$109.10
Purchase #2	$110.27	10.145%	$121.4569	$121.46	$121.45	$121.50
Purchase #3	$127.65	7.734%	$137.5225	$137.52	$137.50	$137.50
Purchase #4	$55.57	7.556%	$59.7689	$59.77	$59.75	$59.80
Purchase #5	$32.50	11.791%	$36.3321	$36.33	$36.35	$36.30
Purchase #6	$109.94	8.788%	$119.6015	$119.60	$119.60	$119.60
Purchase #7	$46.92	4.594%	$49.0755	$49.08	$49.10	$49.10
7 purchase totals =	$579.12		$632.8506	$632.85	$632.85	$632.90