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	$9.82	11.669%	$10.9659	$10.97	$10.95	$11.00
Purchase #2	$59.65	8.841%	$64.9237	$64.92	$64.90	$64.90
Purchase #3	$82.83	4.655%	$86.6857	$86.69	$86.70	$86.70
Purchase #4	$137.37	11.247%	$152.82	$152.82	$152.80	$152.80
Purchase #5	$105.63	5.854%	$111.8136	$111.81	$111.80	$111.80
Purchase #6	$50.41	11.551%	$56.2329	$56.23	$56.25	$56.20
Purchase #7	$102.78	12.793%	$115.9286	$115.93	$115.95	$115.90
7 purchase totals =	$548.49		$599.3704	$599.37	$599.35	$599.30