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	$13.33	13.470%	$15.1256	$15.13	$15.15	$15.10
Purchase #2	$207.92	8.205%	$224.9798	$224.98	$225.00	$225.00
Purchase #3	$12.96	10.106%	$14.2697	$14.27	$14.25	$14.30
Purchase #4	$82.57	9.113%	$90.0946	$90.09	$90.10	$90.10
Purchase #5	$182.77	7.650%	$196.7519	$196.75	$196.75	$196.80
Purchase #6	$89.84	12.467%	$101.0404	$101.04	$101.05	$101.00
Purchase #7	$129.53	12.407%	$145.6008	$145.60	$145.60	$145.60
7 purchase totals =	$718.92		$787.8628	$787.86	$787.90	$787.90