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	$160.59	12.608%	$180.8372	$180.84	$180.85	$180.80
Purchase #2	$228.27	4.426%	$238.3732	$238.37	$238.35	$238.40
Purchase #3	$165.86	11.169%	$184.3849	$184.38	$184.40	$184.40
Purchase #4	$180.35	11.280%	$200.6935	$200.69	$200.70	$200.70
Purchase #5	$143.28	6.466%	$152.5445	$152.54	$152.55	$152.50
Purchase #6	$130.87	10.110%	$144.101	$144.10	$144.10	$144.10
Purchase #7	$140.39	5.863%	$148.6211	$148.62	$148.60	$148.60
7 purchase totals =	$1,149.61		$1,249.5554	$1,249.54	$1,249.55	$1,249.50