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	$80.48	9.726%	$88.3075	$88.31	$88.30	$88.30
Purchase #2	$80.60	10.712%	$89.2339	$89.23	$89.25	$89.20
Purchase #3	$40.75	9.500%	$44.6213	$44.62	$44.60	$44.60
Purchase #4	$105.31	13.734%	$119.7733	$119.77	$119.75	$119.80
Purchase #5	$244.26	4.748%	$255.8575	$255.86	$255.85	$255.90
Purchase #6	$88.66	9.210%	$96.8256	$96.83	$96.85	$96.80
Purchase #7	$138.53	3.671%	$143.6154	$143.62	$143.60	$143.60
7 purchase totals =	$778.59		$838.2345	$838.24	$838.20	$838.20