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	$129.80	9.293%	$141.8623	$141.86	$141.85	$141.90
Purchase #2	$69.45	7.397%	$74.5872	$74.59	$74.60	$74.60
Purchase #3	$236.94	10.143%	$260.9728	$260.97	$260.95	$261.00
Purchase #4	$81.45	9.823%	$89.4508	$89.45	$89.45	$89.50
Purchase #5	$230.58	3.725%	$239.1691	$239.17	$239.15	$239.20
Purchase #6	$157.89	6.547%	$168.2271	$168.23	$168.25	$168.20
Purchase #7	$100.76	5.143%	$105.9421	$105.94	$105.95	$105.90
7 purchase totals =	$1,006.87		$1,080.2114	$1,080.21	$1,080.20	$1,080.30