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	$70.72	10.330%	$78.0254	$78.03	$78.05	$78.00
Purchase #2	$183.37	3.429%	$189.6578	$189.66	$189.65	$189.70
Purchase #3	$56.45	11.166%	$62.7532	$62.75	$62.75	$62.80
Purchase #4	$57.69	4.844%	$60.4845	$60.48	$60.50	$60.50
Purchase #5	$138.66	3.652%	$143.7239	$143.72	$143.70	$143.70
Purchase #6	$90.96	5.125%	$95.6217	$95.62	$95.60	$95.60
Purchase #7	$202.68	10.228%	$223.4101	$223.41	$223.40	$223.40
7 purchase totals =	$800.53		$853.6766	$853.67	$853.65	$853.70