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	$52.81	12.509%	$59.416	$59.42	$59.40	$59.40
Purchase #2	$184.46	8.741%	$200.5836	$200.58	$200.60	$200.60
Purchase #3	$221.61	8.524%	$240.5	$240.50	$240.50	$240.50
Purchase #4	$81.50	4.526%	$85.1887	$85.19	$85.20	$85.20
Purchase #5	$41.54	11.703%	$46.4014	$46.40	$46.40	$46.40
Purchase #6	$137.63	6.484%	$146.5539	$146.55	$146.55	$146.60
Purchase #7	$77.88	5.222%	$81.9469	$81.95	$81.95	$81.90
7 purchase totals =	$797.43		$860.5905	$860.59	$860.60	$860.60