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	$76.28	12.602%	$85.8928	$85.89	$85.90	$85.90
Purchase #2	$87.46	9.114%	$95.4311	$95.43	$95.45	$95.40
Purchase #3	$124.27	7.836%	$134.0078	$134.01	$134.00	$134.00
Purchase #4	$152.85	4.320%	$159.4531	$159.45	$159.45	$159.50
Purchase #5	$146.40	3.367%	$151.3293	$151.33	$151.35	$151.30
Purchase #6	$121.89	4.149%	$126.9472	$126.95	$126.95	$126.90
Purchase #7	$69.50	10.154%	$76.557	$76.56	$76.55	$76.60
7 purchase totals =	$778.65		$829.6183	$829.62	$829.65	$829.60