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	$118.95	6.852%	$127.1005	$127.10	$127.10	$127.10
Purchase #2	$228.59	10.111%	$251.7027	$251.70	$251.70	$251.70
Purchase #3	$71.99	9.142%	$78.5713	$78.57	$78.55	$78.60
Purchase #4	$102.38	9.208%	$111.8072	$111.81	$111.80	$111.80
Purchase #5	$39.50	9.582%	$43.2849	$43.28	$43.30	$43.30
Purchase #6	$113.93	7.211%	$122.1455	$122.15	$122.15	$122.10
Purchase #7	$81.43	6.553%	$86.7661	$86.77	$86.75	$86.80
7 purchase totals =	$756.77		$821.3782	$821.38	$821.35	$821.40