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	$229.92	8.556%	$249.592	$249.59	$249.60	$249.60
Purchase #2	$147.66	13.679%	$167.8584	$167.86	$167.85	$167.90
Purchase #3	$141.81	6.669%	$151.2673	$151.27	$151.25	$151.30
Purchase #4	$215.46	10.522%	$238.1307	$238.13	$238.15	$238.10
Purchase #5	$144.97	6.724%	$154.7178	$154.72	$154.70	$154.70
Purchase #6	$220.71	6.196%	$234.3852	$234.39	$234.40	$234.40
Purchase #7	$106.40	13.250%	$120.498	$120.50	$120.50	$120.50
7 purchase totals =	$1,206.93		$1,316.4494	$1,316.46	$1,316.45	$1,316.50