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	$115.52	12.740%	$130.2372	$130.24	$130.25	$130.20
Purchase #2	$209.35	6.338%	$222.6186	$222.62	$222.60	$222.60
Purchase #3	$80.96	11.866%	$90.5667	$90.57	$90.55	$90.60
Purchase #4	$163.48	8.672%	$177.657	$177.66	$177.65	$177.70
Purchase #5	$232.43	5.103%	$244.2909	$244.29	$244.30	$244.30
Purchase #6	$85.58	6.268%	$90.9442	$90.94	$90.95	$90.90
Purchase #7	$20.57	6.356%	$21.8774	$21.88	$21.90	$21.90
7 purchase totals =	$907.89		$978.1920	$978.20	$978.20	$978.20