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	$80.99	6.302%	$86.094	$86.09	$86.10	$86.10
Purchase #2	$75.63	3.281%	$78.1114	$78.11	$78.10	$78.10
Purchase #3	$56.81	4.463%	$59.3454	$59.35	$59.35	$59.30
Purchase #4	$93.43	9.740%	$102.5301	$102.53	$102.55	$102.50
Purchase #5	$14.53	6.205%	$15.4316	$15.43	$15.45	$15.40
Purchase #6	$122.64	3.724%	$127.2071	$127.21	$127.20	$127.20
Purchase #7	$34.95	10.523%	$38.6278	$38.63	$38.65	$38.60
7 purchase totals =	$478.98		$507.3474	$507.35	$507.40	$507.20