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	$18.60	11.151%	$20.6741	$20.67	$20.65	$20.70
Purchase #2	$77.49	13.554%	$87.993	$87.99	$88.00	$88.00
Purchase #3	$122.29	4.314%	$127.5656	$127.57	$127.55	$127.60
Purchase #4	$206.35	8.329%	$223.5369	$223.54	$223.55	$223.50
Purchase #5	$132.93	6.410%	$141.4508	$141.45	$141.45	$141.50
Purchase #6	$176.98	7.692%	$190.5933	$190.59	$190.60	$190.60
Purchase #7	$11.38	6.144%	$12.0792	$12.08	$12.10	$12.10
7 purchase totals =	$746.02		$803.8929	$803.89	$803.90	$804.00