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	$132.37	13.730%	$150.5444	$150.54	$150.55	$150.50
Purchase #2	$229.60	3.797%	$238.3179	$238.32	$238.30	$238.30
Purchase #3	$56.77	5.656%	$59.9809	$59.98	$60.00	$60.00
Purchase #4	$166.61	7.140%	$178.506	$178.51	$178.50	$178.50
Purchase #5	$160.72	4.873%	$168.5519	$168.55	$168.55	$168.60
Purchase #6	$63.48	4.770%	$66.508	$66.51	$66.50	$66.50
Purchase #7	$80.26	11.646%	$89.6071	$89.61	$89.60	$89.60
7 purchase totals =	$889.81		$952.0162	$952.02	$952.00	$952.00