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	$22.83	6.812%	$24.3852	$24.39	$24.40	$24.40
Purchase #2	$29.53	10.174%	$32.5344	$32.53	$32.55	$32.50
Purchase #3	$179.27	3.606%	$185.7345	$185.73	$185.75	$185.70
Purchase #4	$29.42	8.124%	$31.8101	$31.81	$31.80	$31.80
Purchase #5	$129.92	5.836%	$137.5021	$137.50	$137.50	$137.50
Purchase #6	$23.38	6.518%	$24.9039	$24.90	$24.90	$24.90
Purchase #7	$119.91	7.320%	$128.6874	$128.69	$128.70	$128.70
7 purchase totals =	$534.26		$565.5576	$565.55	$565.60	$565.50