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	$93.81	6.530%	$99.9358	$99.94	$99.95	$99.90
Purchase #2	$109.75	11.680%	$122.5688	$122.57	$122.55	$122.60
Purchase #3	$85.64	5.383%	$90.25	$90.25	$90.25	$90.30
Purchase #4	$25.59	12.351%	$28.7506	$28.75	$28.75	$28.80
Purchase #5	$140.34	10.226%	$154.6912	$154.69	$154.70	$154.70
Purchase #6	$34.33	8.856%	$37.3703	$37.37	$37.35	$37.40
Purchase #7	$19.60	8.600%	$21.2856	$21.29	$21.30	$21.30
7 purchase totals =	$509.06		$554.8523	$554.86	$554.85	$555.00