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	$16.85	12.112%	$18.8909	$18.89	$18.90	$18.90
Purchase #2	$54.72	9.576%	$59.96	$59.96	$59.95	$60.00
Purchase #3	$107.83	5.509%	$113.7704	$113.77	$113.75	$113.80
Purchase #4	$143.43	3.426%	$148.3439	$148.34	$148.35	$148.30
Purchase #5	$67.32	11.816%	$75.2745	$75.27	$75.25	$75.30
Purchase #6	$140.42	13.670%	$159.6154	$159.62	$159.60	$159.60
Purchase #7	$103.48	10.112%	$113.9439	$113.94	$113.95	$113.90
7 purchase totals =	$634.05		$689.7990	$689.79	$689.75	$689.80