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	$76.36	9.380%	$83.5226	$83.52	$83.50	$83.50
Purchase #2	$75.41	13.271%	$85.4177	$85.42	$85.40	$85.40
Purchase #3	$127.76	7.226%	$136.9919	$136.99	$137.00	$137.00
Purchase #4	$42.25	13.747%	$48.0581	$48.06	$48.05	$48.10
Purchase #5	$239.28	12.766%	$269.8265	$269.83	$269.85	$269.80
Purchase #6	$103.54	8.411%	$112.2487	$112.25	$112.25	$112.20
Purchase #7	$110.26	4.792%	$115.5437	$115.54	$115.55	$115.50
7 purchase totals =	$774.86		$851.6092	$851.61	$851.60	$851.50