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	$205.90	10.238%	$226.98	$226.98	$227.00	$227.00
Purchase #2	$149.88	5.438%	$158.0305	$158.03	$158.05	$158.00
Purchase #3	$154.51	11.659%	$172.5243	$172.52	$172.50	$172.50
Purchase #4	$50.64	11.285%	$56.3547	$56.35	$56.35	$56.40
Purchase #5	$187.97	4.454%	$196.3422	$196.34	$196.35	$196.30
Purchase #6	$160.64	8.284%	$173.9474	$173.95	$173.95	$173.90
Purchase #7	$9.31	9.859%	$10.2279	$10.23	$10.25	$10.20
7 purchase totals =	$918.85		$994.4070	$994.40	$994.45	$994.30