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	$24.81	3.401%	$25.6538	$25.65	$25.65	$25.70
Purchase #2	$109.88	6.344%	$116.8508	$116.85	$116.85	$116.90
Purchase #3	$80.34	13.103%	$90.867	$90.87	$90.85	$90.90
Purchase #4	$21.67	11.832%	$24.234	$24.23	$24.25	$24.20
Purchase #5	$214.57	13.319%	$243.1486	$243.15	$243.15	$243.10
Purchase #6	$109.94	10.262%	$121.222	$121.22	$121.20	$121.20
Purchase #7	$26.61	7.587%	$28.6289	$28.63	$28.65	$28.60
7 purchase totals =	$587.82		$650.6051	$650.60	$650.60	$650.60