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	$160.36	3.327%	$165.6952	$165.70	$165.70	$165.70
Purchase #2	$99.79	8.111%	$107.884	$107.88	$107.90	$107.90
Purchase #3	$130.84	7.595%	$140.7773	$140.78	$140.80	$140.80
Purchase #4	$59.35	7.406%	$63.7455	$63.75	$63.75	$63.70
Purchase #5	$241.65	13.394%	$274.0166	$274.02	$274.00	$274.00
Purchase #6	$131.52	4.509%	$137.4502	$137.45	$137.45	$137.50
Purchase #7	$182.76	7.395%	$196.2751	$196.28	$196.30	$196.30
7 purchase totals =	$1,006.27		$1,085.8439	$1,085.86	$1,085.90	$1,085.90