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	$239.69	6.594%	$255.4952	$255.50	$255.50	$255.50
Purchase #2	$108.25	6.800%	$115.611	$115.61	$115.60	$115.60
Purchase #3	$96.88	13.434%	$109.8949	$109.89	$109.90	$109.90
Purchase #4	$106.50	12.273%	$119.5707	$119.57	$119.55	$119.60
Purchase #5	$24.27	4.231%	$25.2969	$25.30	$25.30	$25.30
Purchase #6	$225.47	8.562%	$244.7747	$244.77	$244.75	$244.80
Purchase #7	$107.46	10.569%	$118.8174	$118.82	$118.80	$118.80
7 purchase totals =	$908.52		$989.4608	$989.46	$989.40	$989.50