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	$9.79	9.509%	$10.7209	$10.72	$10.70	$10.70
Purchase #2	$47.46	10.311%	$52.3536	$52.35	$52.35	$52.40
Purchase #3	$103.69	4.587%	$108.4463	$108.45	$108.45	$108.40
Purchase #4	$249.67	10.613%	$276.1675	$276.17	$276.15	$276.20
Purchase #5	$7.64	4.131%	$7.9556	$7.96	$7.95	$8.00
Purchase #6	$128.50	7.218%	$137.7751	$137.78	$137.80	$137.80
Purchase #7	$33.58	11.832%	$37.5532	$37.55	$37.55	$37.60
7 purchase totals =	$580.33		$630.9722	$630.98	$630.95	$631.10