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	$229.50	10.500%	$253.5975	$253.60	$253.60	$253.60
Purchase #2	$212.97	7.778%	$229.5348	$229.53	$229.55	$229.50
Purchase #3	$145.91	7.738%	$157.2005	$157.20	$157.20	$157.20
Purchase #4	$163.51	9.360%	$178.8145	$178.81	$178.80	$178.80
Purchase #5	$41.71	4.449%	$43.5657	$43.57	$43.55	$43.60
Purchase #6	$59.33	11.380%	$66.0818	$66.08	$66.10	$66.10
Purchase #7	$104.66	6.214%	$111.1636	$111.16	$111.15	$111.20
7 purchase totals =	$957.59		$1,039.9584	$1,039.95	$1,039.95	$1,040.00