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	$46.65	10.712%	$51.6471	$51.65	$51.65	$51.60
Purchase #2	$95.71	11.370%	$106.5922	$106.59	$106.60	$106.60
Purchase #3	$45.80	6.154%	$48.6185	$48.62	$48.60	$48.60
Purchase #4	$59.78	4.793%	$62.6453	$62.65	$62.65	$62.60
Purchase #5	$52.81	5.439%	$55.6823	$55.68	$55.70	$55.70
Purchase #6	$46.30	8.804%	$50.3763	$50.38	$50.40	$50.40
Purchase #7	$233.34	11.349%	$259.8218	$259.82	$259.80	$259.80
7 purchase totals =	$580.39		$635.3835	$635.39	$635.40	$635.30