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	$113.60	9.607%	$124.5136	$124.51	$124.50	$124.50
Purchase #2	$49.65	3.407%	$51.3416	$51.34	$51.35	$51.30
Purchase #3	$205.89	9.385%	$225.2128	$225.21	$225.20	$225.20
Purchase #4	$34.86	11.354%	$38.818	$38.82	$38.80	$38.80
Purchase #5	$43.32	4.686%	$45.35	$45.35	$45.35	$45.40
Purchase #6	$125.45	7.245%	$134.5389	$134.54	$134.55	$134.50
Purchase #7	$44.65	5.757%	$47.2205	$47.22	$47.20	$47.20
7 purchase totals =	$617.42		$666.9954	$666.99	$666.95	$666.90