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	$52.64	12.577%	$59.2605	$59.26	$59.25	$59.30
Purchase #2	$36.82	8.759%	$40.0451	$40.05	$40.05	$40.00
Purchase #3	$78.27	4.451%	$81.7538	$81.75	$81.75	$81.80
Purchase #4	$212.53	10.315%	$234.4525	$234.45	$234.45	$234.50
Purchase #5	$39.49	8.678%	$42.9169	$42.92	$42.90	$42.90
Purchase #6	$44.55	11.317%	$49.5917	$49.59	$49.60	$49.60
Purchase #7	$46.27	11.262%	$51.4809	$51.48	$51.50	$51.50
7 purchase totals =	$510.57		$559.5014	$559.50	$559.50	$559.60