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	$64.42	12.527%	$72.4899	$72.49	$72.50	$72.50
Purchase #2	$208.75	10.853%	$231.4056	$231.41	$231.40	$231.40
Purchase #3	$145.81	8.544%	$158.268	$158.27	$158.25	$158.30
Purchase #4	$105.64	3.751%	$109.6026	$109.60	$109.60	$109.60
Purchase #5	$195.72	8.806%	$212.9551	$212.96	$212.95	$213.00
Purchase #6	$107.30	13.678%	$121.9765	$121.98	$122.00	$122.00
Purchase #7	$80.85	11.861%	$90.4396	$90.44	$90.45	$90.40
7 purchase totals =	$908.49		$997.1373	$997.15	$997.15	$997.20