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	$31.47	8.562%	$34.1645	$34.16	$34.15	$34.20
Purchase #2	$214.41	9.378%	$234.5174	$234.52	$234.50	$234.50
Purchase #3	$36.60	8.838%	$39.8347	$39.83	$39.85	$39.80
Purchase #4	$49.70	13.860%	$56.5884	$56.59	$56.60	$56.60
Purchase #5	$237.71	7.218%	$254.8679	$254.87	$254.85	$254.90
Purchase #6	$169.40	12.322%	$190.2735	$190.27	$190.25	$190.30
Purchase #7	$237.28	5.746%	$250.9141	$250.91	$250.90	$250.90
7 purchase totals =	$976.57		$1,061.1605	$1,061.15	$1,061.10	$1,061.20