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	$81.44	5.715%	$86.0943	$86.09	$86.10	$86.10
Purchase #2	$56.27	6.368%	$59.8533	$59.85	$59.85	$59.90
Purchase #3	$36.69	8.647%	$39.8626	$39.86	$39.85	$39.90
Purchase #4	$47.93	3.653%	$49.6809	$49.68	$49.70	$49.70
Purchase #5	$81.43	9.688%	$89.3189	$89.32	$89.30	$89.30
Purchase #6	$137.79	10.630%	$152.4371	$152.44	$152.45	$152.40
Purchase #7	$18.95	11.234%	$21.0788	$21.08	$21.10	$21.10
7 purchase totals =	$460.50		$498.3259	$498.32	$498.35	$498.40