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	$124.66	12.649%	$140.4282	$140.43	$140.45	$140.40
Purchase #2	$52.86	12.657%	$59.5505	$59.55	$59.55	$59.60
Purchase #3	$92.42	12.139%	$103.6389	$103.64	$103.65	$103.60
Purchase #4	$140.68	13.189%	$159.2343	$159.23	$159.25	$159.20
Purchase #5	$124.72	11.416%	$138.958	$138.96	$138.95	$139.00
Purchase #6	$43.38	10.561%	$47.9614	$47.96	$47.95	$48.00
Purchase #7	$184.60	3.173%	$190.4574	$190.46	$190.45	$190.50
7 purchase totals =	$763.32		$840.2287	$840.23	$840.25	$840.30