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	$87.52	3.639%	$90.7049	$90.70	$90.70	$90.70
Purchase #2	$51.59	9.687%	$56.5875	$56.59	$56.60	$56.60
Purchase #3	$105.76	5.490%	$111.5662	$111.57	$111.55	$111.60
Purchase #4	$204.28	7.501%	$219.603	$219.60	$219.60	$219.60
Purchase #5	$238.42	8.589%	$258.8979	$258.90	$258.90	$258.90
Purchase #6	$206.37	4.518%	$215.6938	$215.69	$215.70	$215.70
Purchase #7	$47.90	8.147%	$51.8024	$51.80	$51.80	$51.80
7 purchase totals =	$941.84		$1,004.8557	$1,004.85	$1,004.85	$1,004.90