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	$82.89	7.853%	$89.3994	$89.40	$89.40	$89.40
Purchase #2	$193.89	10.742%	$214.7177	$214.72	$214.70	$214.70
Purchase #3	$97.32	8.164%	$105.2652	$105.27	$105.25	$105.30
Purchase #4	$210.62	10.434%	$232.5961	$232.60	$232.60	$232.60
Purchase #5	$41.86	11.455%	$46.6551	$46.66	$46.65	$46.70
Purchase #6	$144.43	4.424%	$150.8196	$150.82	$150.80	$150.80
Purchase #7	$66.68	5.179%	$70.1334	$70.13	$70.15	$70.10
7 purchase totals =	$837.69		$909.5865	$909.60	$909.55	$909.60