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	$244.32	10.722%	$270.516	$270.52	$270.50	$270.50
Purchase #2	$39.79	10.858%	$44.1104	$44.11	$44.10	$44.10
Purchase #3	$53.70	3.552%	$55.6074	$55.61	$55.60	$55.60
Purchase #4	$246.99	3.419%	$255.4346	$255.43	$255.45	$255.40
Purchase #5	$132.78	10.283%	$146.4338	$146.43	$146.45	$146.40
Purchase #6	$99.65	5.505%	$105.1357	$105.14	$105.15	$105.10
Purchase #7	$86.47	4.853%	$90.6664	$90.67	$90.65	$90.70
7 purchase totals =	$903.70		$967.9043	$967.91	$967.90	$967.80