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	$27.51	5.456%	$29.0109	$29.01	$29.00	$29.00
Purchase #2	$241.98	13.290%	$274.1391	$274.14	$274.15	$274.10
Purchase #3	$34.80	7.342%	$37.355	$37.36	$37.35	$37.40
Purchase #4	$174.60	3.822%	$181.2732	$181.27	$181.25	$181.30
Purchase #5	$234.51	4.245%	$244.4649	$244.46	$244.45	$244.50
Purchase #6	$105.75	5.541%	$111.6096	$111.61	$111.60	$111.60
Purchase #7	$36.31	5.349%	$38.2522	$38.25	$38.25	$38.30
7 purchase totals =	$855.46		$916.1049	$916.10	$916.05	$916.20