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	$73.78	11.722%	$82.4285	$82.43	$82.45	$82.40
Purchase #2	$85.67	12.545%	$96.4173	$96.42	$96.40	$96.40
Purchase #3	$62.31	5.710%	$65.8679	$65.87	$65.85	$65.90
Purchase #4	$29.61	9.530%	$32.4318	$32.43	$32.45	$32.40
Purchase #5	$162.70	13.751%	$185.0729	$185.07	$185.05	$185.10
Purchase #6	$107.99	3.189%	$111.4338	$111.43	$111.45	$111.40
Purchase #7	$217.34	13.521%	$246.7265	$246.73	$246.75	$246.70
7 purchase totals =	$739.40		$820.3787	$820.38	$820.40	$820.30