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	$39.86	6.530%	$42.4629	$42.46	$42.45	$42.50
Purchase #2	$29.26	11.129%	$32.5163	$32.52	$32.50	$32.50
Purchase #3	$195.75	7.604%	$210.6348	$210.63	$210.65	$210.60
Purchase #4	$170.59	11.652%	$190.4671	$190.47	$190.45	$190.50
Purchase #5	$8.64	4.492%	$9.0281	$9.03	$9.05	$9.00
Purchase #6	$219.64	7.183%	$235.4167	$235.42	$235.40	$235.40
Purchase #7	$20.46	6.443%	$21.7782	$21.78	$21.80	$21.80
7 purchase totals =	$684.20		$742.3041	$742.31	$742.30	$742.30