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	$205.86	12.558%	$231.7119	$231.71	$231.70	$231.70
Purchase #2	$141.45	10.833%	$156.7733	$156.77	$156.75	$156.80
Purchase #3	$38.78	4.665%	$40.5891	$40.59	$40.60	$40.60
Purchase #4	$67.49	7.786%	$72.7448	$72.74	$72.75	$72.70
Purchase #5	$110.45	10.841%	$122.4239	$122.42	$122.40	$122.40
Purchase #6	$156.36	4.819%	$163.895	$163.90	$163.90	$163.90
Purchase #7	$87.52	3.761%	$90.8116	$90.81	$90.80	$90.80
7 purchase totals =	$807.91		$878.9496	$878.94	$878.90	$878.90