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	$159.91	10.649%	$176.9388	$176.94	$176.95	$176.90
Purchase #2	$159.81	5.167%	$168.0674	$168.07	$168.05	$168.10
Purchase #3	$206.38	11.838%	$230.8113	$230.81	$230.80	$230.80
Purchase #4	$128.34	10.234%	$141.4743	$141.47	$141.45	$141.50
Purchase #5	$181.33	3.362%	$187.4263	$187.43	$187.45	$187.40
Purchase #6	$100.97	10.485%	$111.5567	$111.56	$111.55	$111.60
Purchase #7	$20.58	6.471%	$21.9117	$21.91	$21.90	$21.90
7 purchase totals =	$957.32		$1,038.1865	$1,038.19	$1,038.15	$1,038.20