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	$152.55	5.340%	$160.6962	$160.70	$160.70	$160.70
Purchase #2	$78.66	9.283%	$85.962	$85.96	$85.95	$86.00
Purchase #3	$65.59	6.419%	$69.8002	$69.80	$69.80	$69.80
Purchase #4	$75.58	3.516%	$78.2374	$78.24	$78.25	$78.20
Purchase #5	$127.83	12.629%	$143.9737	$143.97	$143.95	$144.00
Purchase #6	$59.86	4.800%	$62.7333	$62.73	$62.75	$62.70
Purchase #7	$105.39	10.518%	$116.4749	$116.47	$116.45	$116.50
7 purchase totals =	$665.46		$717.8777	$717.87	$717.85	$717.90