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	$90.55	7.509%	$97.3494	$97.35	$97.35	$97.30
Purchase #2	$104.37	3.358%	$107.8747	$107.87	$107.85	$107.90
Purchase #3	$49.96	13.314%	$56.6117	$56.61	$56.60	$56.60
Purchase #4	$66.28	9.415%	$72.5203	$72.52	$72.50	$72.50
Purchase #5	$28.41	8.318%	$30.7731	$30.77	$30.75	$30.80
Purchase #6	$206.35	5.841%	$218.4029	$218.40	$218.40	$218.40
Purchase #7	$76.53	7.677%	$82.4052	$82.41	$82.40	$82.40
7 purchase totals =	$622.45		$665.9373	$665.93	$665.85	$665.90