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	$56.92	4.335%	$59.3875	$59.39	$59.40	$59.40
Purchase #2	$214.80	10.452%	$237.2509	$237.25	$237.25	$237.30
Purchase #3	$26.34	8.389%	$28.5497	$28.55	$28.55	$28.50
Purchase #4	$19.34	4.489%	$20.2082	$20.21	$20.20	$20.20
Purchase #5	$28.92	8.684%	$31.4314	$31.43	$31.45	$31.40
Purchase #6	$41.94	6.303%	$44.5835	$44.58	$44.60	$44.60
Purchase #7	$200.63	9.675%	$220.041	$220.04	$220.05	$220.00
7 purchase totals =	$588.89		$641.4522	$641.45	$641.50	$641.40