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	$206.73	4.205%	$215.423	$215.42	$215.40	$215.40
Purchase #2	$134.58	4.642%	$140.8272	$140.83	$140.85	$140.80
Purchase #3	$152.83	4.345%	$159.4705	$159.47	$159.45	$159.50
Purchase #4	$99.35	10.503%	$109.7847	$109.78	$109.80	$109.80
Purchase #5	$163.29	11.774%	$182.5158	$182.52	$182.50	$182.50
Purchase #6	$245.38	6.291%	$260.8169	$260.82	$260.80	$260.80
Purchase #7	$220.43	4.709%	$230.81	$230.81	$230.80	$230.80
7 purchase totals =	$1,222.59		$1,299.6481	$1,299.65	$1,299.60	$1,299.60