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	$19.85	5.874%	$21.016	$21.02	$21.00	$21.00
Purchase #2	$243.83	5.433%	$257.0773	$257.08	$257.10	$257.10
Purchase #3	$233.25	13.509%	$264.7597	$264.76	$264.75	$264.80
Purchase #4	$199.52	6.242%	$211.974	$211.97	$211.95	$212.00
Purchase #5	$6.92	7.186%	$7.4173	$7.42	$7.40	$7.40
Purchase #6	$119.94	9.699%	$131.573	$131.57	$131.55	$131.60
Purchase #7	$233.96	9.749%	$256.7688	$256.77	$256.75	$256.80
7 purchase totals =	$1,057.27		$1,150.5861	$1,150.59	$1,150.50	$1,150.70