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	$92.78	12.847%	$104.6994	$104.70	$104.70	$104.70
Purchase #2	$59.95	11.429%	$66.8017	$66.80	$66.80	$66.80
Purchase #3	$232.40	10.849%	$257.6131	$257.61	$257.60	$257.60
Purchase #4	$27.82	12.415%	$31.2739	$31.27	$31.25	$31.30
Purchase #5	$76.78	11.357%	$85.4999	$85.50	$85.50	$85.50
Purchase #6	$200.25	5.529%	$211.3218	$211.32	$211.30	$211.30
Purchase #7	$108.78	13.624%	$123.6002	$123.60	$123.60	$123.60
7 purchase totals =	$798.76		$880.8100	$880.80	$880.75	$880.80