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	$229.58	11.477%	$255.9289	$255.93	$255.95	$255.90
Purchase #2	$34.85	11.471%	$38.8476	$38.85	$38.85	$38.80
Purchase #3	$166.88	11.555%	$186.163	$186.16	$186.15	$186.20
Purchase #4	$25.40	8.545%	$27.5704	$27.57	$27.55	$27.60
Purchase #5	$51.64	10.464%	$57.0436	$57.04	$57.05	$57.00
Purchase #6	$40.72	13.761%	$46.3235	$46.32	$46.30	$46.30
Purchase #7	$31.83	10.803%	$35.2686	$35.27	$35.25	$35.30
7 purchase totals =	$580.90		$647.1456	$647.14	$647.10	$647.10