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	$35.40	13.847%	$40.3018	$40.30	$40.30	$40.30
Purchase #2	$5.39	7.138%	$5.7747	$5.77	$5.75	$5.80
Purchase #3	$131.78	7.820%	$142.0852	$142.09	$142.10	$142.10
Purchase #4	$151.93	4.320%	$158.4934	$158.49	$158.50	$158.50
Purchase #5	$68.99	12.763%	$77.7952	$77.80	$77.80	$77.80
Purchase #6	$32.82	3.151%	$33.8542	$33.85	$33.85	$33.90
Purchase #7	$59.57	7.131%	$63.8179	$63.82	$63.80	$63.80
7 purchase totals =	$485.88		$522.1224	$522.12	$522.10	$522.20