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	$34.44	3.333%	$35.5879	$35.59	$35.60	$35.60
Purchase #2	$192.80	10.650%	$213.3332	$213.33	$213.35	$213.30
Purchase #3	$205.30	8.281%	$222.3009	$222.30	$222.30	$222.30
Purchase #4	$113.78	5.149%	$119.6385	$119.64	$119.65	$119.60
Purchase #5	$116.39	12.495%	$130.9329	$130.93	$130.95	$130.90
Purchase #6	$163.30	10.521%	$180.4808	$180.48	$180.50	$180.50
Purchase #7	$44.49	11.229%	$49.4858	$49.49	$49.50	$49.50
7 purchase totals =	$870.50		$951.7600	$951.76	$951.85	$951.70