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	$113.55	13.524%	$128.9065	$128.91	$128.90	$128.90
Purchase #2	$219.25	6.714%	$233.9704	$233.97	$233.95	$234.00
Purchase #3	$221.55	5.566%	$233.8815	$233.88	$233.90	$233.90
Purchase #4	$152.78	9.329%	$167.0328	$167.03	$167.05	$167.00
Purchase #5	$100.71	5.181%	$105.9278	$105.93	$105.95	$105.90
Purchase #6	$205.64	12.348%	$231.0324	$231.03	$231.05	$231.00
Purchase #7	$121.39	9.181%	$132.5348	$132.53	$132.55	$132.50
7 purchase totals =	$1,134.87		$1,233.2862	$1,233.28	$1,233.35	$1,233.20