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	$78.86	8.392%	$85.4779	$85.48	$85.50	$85.50
Purchase #2	$132.26	10.168%	$145.7082	$145.71	$145.70	$145.70
Purchase #3	$175.78	6.666%	$187.4975	$187.50	$187.50	$187.50
Purchase #4	$131.64	8.803%	$143.2283	$143.23	$143.25	$143.20
Purchase #5	$22.57	4.636%	$23.6163	$23.62	$23.60	$23.60
Purchase #6	$54.30	8.820%	$59.0893	$59.09	$59.10	$59.10
Purchase #7	$159.26	5.500%	$168.0193	$168.02	$168.00	$168.00
7 purchase totals =	$754.67		$812.6368	$812.65	$812.65	$812.60