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	$238.39	13.755%	$271.1805	$271.18	$271.20	$271.20
Purchase #2	$18.45	4.116%	$19.2094	$19.21	$19.20	$19.20
Purchase #3	$21.75	10.446%	$24.022	$24.02	$24.00	$24.00
Purchase #4	$52.93	12.649%	$59.6251	$59.63	$59.65	$59.60
Purchase #5	$51.90	4.678%	$54.3279	$54.33	$54.35	$54.30
Purchase #6	$144.77	9.145%	$158.0092	$158.01	$158.00	$158.00
Purchase #7	$18.86	8.294%	$20.4242	$20.42	$20.40	$20.40
7 purchase totals =	$547.05		$606.7983	$606.80	$606.80	$606.70