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	$36.83	13.793%	$41.91	$41.91	$41.90	$41.90
Purchase #2	$137.33	9.389%	$150.2239	$150.22	$150.20	$150.20
Purchase #3	$177.80	8.503%	$192.9183	$192.92	$192.90	$192.90
Purchase #4	$43.54	5.522%	$45.9443	$45.94	$45.95	$45.90
Purchase #5	$12.27	10.155%	$13.516	$13.52	$13.50	$13.50
Purchase #6	$160.25	9.820%	$175.9866	$175.99	$176.00	$176.00
Purchase #7	$153.51	8.393%	$166.3941	$166.39	$166.40	$166.40
7 purchase totals =	$721.53		$786.8932	$786.89	$786.85	$786.80