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	$8.92	10.234%	$9.8329	$9.83	$9.85	$9.80
Purchase #2	$59.98	12.854%	$67.6898	$67.69	$67.70	$67.70
Purchase #3	$139.82	4.298%	$145.8295	$145.83	$145.85	$145.80
Purchase #4	$204.86	11.340%	$228.0911	$228.09	$228.10	$228.10
Purchase #5	$88.30	9.621%	$96.7953	$96.80	$96.80	$96.80
Purchase #6	$241.85	8.413%	$262.1968	$262.20	$262.20	$262.20
Purchase #7	$158.38	6.363%	$168.4577	$168.46	$168.45	$168.50
7 purchase totals =	$902.11		$978.8931	$978.90	$978.95	$978.90