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	$118.87	10.644%	$131.5225	$131.52	$131.50	$131.50
Purchase #2	$205.83	3.776%	$213.6021	$213.60	$213.60	$213.60
Purchase #3	$98.80	12.440%	$111.0907	$111.09	$111.10	$111.10
Purchase #4	$46.78	3.790%	$48.553	$48.55	$48.55	$48.60
Purchase #5	$237.95	4.637%	$248.9837	$248.98	$249.00	$249.00
Purchase #6	$168.94	12.655%	$190.3194	$190.32	$190.30	$190.30
Purchase #7	$14.34	8.871%	$15.6121	$15.61	$15.60	$15.60
7 purchase totals =	$891.51		$959.6835	$959.67	$959.65	$959.70