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	$37.37	6.653%	$39.8562	$39.86	$39.85	$39.90
Purchase #2	$219.81	7.851%	$237.0673	$237.07	$237.05	$237.10
Purchase #3	$103.38	8.108%	$111.7621	$111.76	$111.75	$111.80
Purchase #4	$76.62	13.628%	$87.0618	$87.06	$87.05	$87.10
Purchase #5	$145.63	7.428%	$156.4474	$156.45	$156.45	$156.40
Purchase #6	$233.26	12.149%	$261.5988	$261.60	$261.60	$261.60
Purchase #7	$191.86	4.733%	$200.9407	$200.94	$200.95	$200.90
7 purchase totals =	$1,007.93		$1,094.7343	$1,094.74	$1,094.70	$1,094.80