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	$20.98	7.119%	$22.4736	$22.47	$22.45	$22.50
Purchase #2	$18.78	8.181%	$20.3164	$20.32	$20.30	$20.30
Purchase #3	$19.68	4.625%	$20.5902	$20.59	$20.60	$20.60
Purchase #4	$142.65	11.323%	$158.8023	$158.80	$158.80	$158.80
Purchase #5	$87.88	5.720%	$92.9067	$92.91	$92.90	$92.90
Purchase #6	$143.94	10.130%	$158.5211	$158.52	$158.50	$158.50
Purchase #7	$135.48	4.307%	$141.3151	$141.32	$141.30	$141.30
7 purchase totals =	$569.39		$614.9254	$614.93	$614.85	$614.90