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	$146.51	6.733%	$156.3745	$156.37	$156.35	$156.40
Purchase #2	$126.57	12.193%	$142.0027	$142.00	$142.00	$142.00
Purchase #3	$50.52	8.322%	$54.7243	$54.72	$54.70	$54.70
Purchase #4	$209.59	8.512%	$227.4303	$227.43	$227.45	$227.40
Purchase #5	$111.48	5.654%	$117.7831	$117.78	$117.80	$117.80
Purchase #6	$52.43	5.592%	$55.3619	$55.36	$55.35	$55.40
Purchase #7	$103.83	10.815%	$115.0592	$115.06	$115.05	$115.10
7 purchase totals =	$800.93		$868.7360	$868.72	$868.70	$868.80