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	$41.34	9.193%	$45.1404	$45.14	$45.15	$45.10
Purchase #2	$30.85	5.127%	$32.4317	$32.43	$32.45	$32.40
Purchase #3	$123.50	13.770%	$140.506	$140.51	$140.50	$140.50
Purchase #4	$129.37	6.350%	$137.585	$137.59	$137.60	$137.60
Purchase #5	$118.81	6.678%	$126.7441	$126.74	$126.75	$126.70
Purchase #6	$19.73	10.685%	$21.8382	$21.84	$21.85	$21.80
Purchase #7	$76.96	9.754%	$84.4667	$84.47	$84.45	$84.50
7 purchase totals =	$540.56		$588.7121	$588.72	$588.75	$588.60