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	$120.56	10.176%	$132.8282	$132.83	$132.85	$132.80
Purchase #2	$81.75	4.490%	$85.4206	$85.42	$85.40	$85.40
Purchase #3	$97.89	8.195%	$105.9121	$105.91	$105.90	$105.90
Purchase #4	$228.48	5.244%	$240.4615	$240.46	$240.45	$240.50
Purchase #5	$48.48	5.105%	$50.9549	$50.95	$50.95	$51.00
Purchase #6	$133.65	12.582%	$150.4658	$150.47	$150.45	$150.50
Purchase #7	$39.65	10.215%	$43.7002	$43.70	$43.70	$43.70
7 purchase totals =	$750.46		$809.7433	$809.74	$809.70	$809.80