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	$138.34	13.814%	$157.4503	$157.45	$157.45	$157.50
Purchase #2	$202.82	6.300%	$215.5977	$215.60	$215.60	$215.60
Purchase #3	$137.86	9.168%	$150.499	$150.50	$150.50	$150.50
Purchase #4	$53.90	9.638%	$59.0949	$59.09	$59.10	$59.10
Purchase #5	$177.81	4.575%	$185.9448	$185.94	$185.95	$185.90
Purchase #6	$73.45	8.359%	$79.5897	$79.59	$79.60	$79.60
Purchase #7	$103.58	9.540%	$113.4615	$113.46	$113.45	$113.50
7 purchase totals =	$887.76		$961.6379	$961.63	$961.65	$961.70