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	$249.72	5.735%	$264.0414	$264.04	$264.05	$264.00
Purchase #2	$23.75	5.626%	$25.0862	$25.09	$25.10	$25.10
Purchase #3	$75.96	12.596%	$85.5279	$85.53	$85.55	$85.50
Purchase #4	$66.41	9.574%	$72.7681	$72.77	$72.75	$72.80
Purchase #5	$178.82	4.491%	$186.8508	$186.85	$186.85	$186.90
Purchase #6	$158.66	13.388%	$179.9014	$179.90	$179.90	$179.90
Purchase #7	$217.64	6.482%	$231.7474	$231.75	$231.75	$231.70
7 purchase totals =	$970.96		$1,045.9232	$1,045.93	$1,045.95	$1,045.90