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	$74.76	10.455%	$82.5762	$82.58	$82.60	$82.60
Purchase #2	$26.55	9.546%	$29.0845	$29.08	$29.10	$29.10
Purchase #3	$76.98	12.307%	$86.4539	$86.45	$86.45	$86.50
Purchase #4	$105.72	11.318%	$117.6854	$117.69	$117.70	$117.70
Purchase #5	$208.29	8.258%	$225.4906	$225.49	$225.50	$225.50
Purchase #6	$138.49	12.678%	$156.0478	$156.05	$156.05	$156.00
Purchase #7	$81.97	11.179%	$91.1334	$91.13	$91.15	$91.10
7 purchase totals =	$712.76		$788.4718	$788.47	$788.55	$788.50