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	$44.77	13.542%	$50.8328	$50.83	$50.85	$50.80
Purchase #2	$161.28	5.281%	$169.7972	$169.80	$169.80	$169.80
Purchase #3	$8.97	7.531%	$9.6455	$9.65	$9.65	$9.60
Purchase #4	$225.87	13.214%	$255.7165	$255.72	$255.70	$255.70
Purchase #5	$129.90	7.432%	$139.5542	$139.55	$139.55	$139.60
Purchase #6	$209.55	13.823%	$238.5161	$238.52	$238.50	$238.50
Purchase #7	$102.69	8.601%	$111.5224	$111.52	$111.50	$111.50
7 purchase totals =	$883.03		$975.5847	$975.59	$975.55	$975.50