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	$11.99	12.252%	$13.459	$13.46	$13.45	$13.50
Purchase #2	$103.60	10.867%	$114.8582	$114.86	$114.85	$114.90
Purchase #3	$13.54	9.540%	$14.8317	$14.83	$14.85	$14.80
Purchase #4	$85.94	4.519%	$89.8236	$89.82	$89.80	$89.80
Purchase #5	$40.40	9.270%	$44.1451	$44.15	$44.15	$44.10
Purchase #6	$199.87	11.187%	$222.2295	$222.23	$222.25	$222.20
Purchase #7	$229.90	5.185%	$241.8203	$241.82	$241.80	$241.80
7 purchase totals =	$685.24		$741.1674	$741.17	$741.15	$741.10