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	$156.25	9.292%	$170.7688	$170.77	$170.75	$170.80
Purchase #2	$93.83	5.758%	$99.2327	$99.23	$99.25	$99.20
Purchase #3	$27.85	5.553%	$29.3965	$29.40	$29.40	$29.40
Purchase #4	$35.91	3.479%	$37.1593	$37.16	$37.15	$37.20
Purchase #5	$41.81	8.233%	$45.2522	$45.25	$45.25	$45.30
Purchase #6	$11.51	4.342%	$12.0098	$12.01	$12.00	$12.00
Purchase #7	$203.46	9.420%	$222.6259	$222.63	$222.65	$222.60
7 purchase totals =	$570.62		$616.4452	$616.45	$616.45	$616.50