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	$140.38	10.426%	$155.016	$155.02	$155.00	$155.00
Purchase #2	$125.49	9.484%	$137.3915	$137.39	$137.40	$137.40
Purchase #3	$190.84	5.247%	$200.8534	$200.85	$200.85	$200.90
Purchase #4	$67.98	4.281%	$70.8902	$70.89	$70.90	$70.90
Purchase #5	$246.67	9.643%	$270.4564	$270.46	$270.45	$270.50
Purchase #6	$18.86	4.507%	$19.71	$19.71	$19.70	$19.70
Purchase #7	$111.67	3.498%	$115.5762	$115.58	$115.60	$115.60
7 purchase totals =	$901.89		$969.8937	$969.90	$969.90	$970.00