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	$100.49	11.557%	$112.1036	$112.10	$112.10	$112.10
Purchase #2	$154.65	13.265%	$175.1643	$175.16	$175.15	$175.20
Purchase #3	$90.79	10.871%	$100.6598	$100.66	$100.65	$100.70
Purchase #4	$66.64	8.829%	$72.5236	$72.52	$72.50	$72.50
Purchase #5	$134.88	11.809%	$150.808	$150.81	$150.80	$150.80
Purchase #6	$16.99	12.502%	$19.1141	$19.11	$19.10	$19.10
Purchase #7	$25.70	8.603%	$27.911	$27.91	$27.90	$27.90
7 purchase totals =	$590.14		$658.2844	$658.27	$658.20	$658.30