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	$180.83	3.809%	$187.7178	$187.72	$187.70	$187.70
Purchase #2	$138.94	12.610%	$156.4603	$156.46	$156.45	$156.50
Purchase #3	$208.75	10.859%	$231.4182	$231.42	$231.40	$231.40
Purchase #4	$27.57	5.358%	$29.0472	$29.05	$29.05	$29.00
Purchase #5	$128.56	4.841%	$134.7836	$134.78	$134.80	$134.80
Purchase #6	$77.49	10.190%	$85.3862	$85.39	$85.40	$85.40
Purchase #7	$59.79	4.822%	$62.6731	$62.67	$62.65	$62.70
7 purchase totals =	$821.93		$887.4864	$887.49	$887.45	$887.50