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	$73.47	12.767%	$82.8499	$82.85	$82.85	$82.80
Purchase #2	$83.91	5.439%	$88.4739	$88.47	$88.45	$88.50
Purchase #3	$7.65	11.286%	$8.5134	$8.51	$8.50	$8.50
Purchase #4	$189.58	5.531%	$200.0657	$200.07	$200.05	$200.10
Purchase #5	$54.71	3.285%	$56.5072	$56.51	$56.50	$56.50
Purchase #6	$42.75	7.401%	$45.9139	$45.91	$45.90	$45.90
Purchase #7	$89.51	8.725%	$97.3197	$97.32	$97.30	$97.30
7 purchase totals =	$541.58		$579.6437	$579.64	$579.55	$579.60