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	$60.28	13.643%	$68.504	$68.50	$68.50	$68.50
Purchase #2	$80.73	13.755%	$91.8344	$91.83	$91.85	$91.80
Purchase #3	$240.75	10.675%	$266.4501	$266.45	$266.45	$266.50
Purchase #4	$231.35	9.434%	$253.1756	$253.18	$253.20	$253.20
Purchase #5	$219.79	6.872%	$234.894	$234.89	$234.90	$234.90
Purchase #6	$156.49	7.756%	$168.6274	$168.63	$168.65	$168.60
Purchase #7	$186.83	5.189%	$196.5246	$196.52	$196.50	$196.50
7 purchase totals =	$1,176.22		$1,280.0101	$1,280.00	$1,280.05	$1,280.00