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	$236.30	8.481%	$256.3406	$256.34	$256.35	$256.30
Purchase #2	$136.32	13.226%	$154.3497	$154.35	$154.35	$154.30
Purchase #3	$53.72	9.145%	$58.6327	$58.63	$58.65	$58.60
Purchase #4	$71.78	9.145%	$78.3443	$78.34	$78.35	$78.30
Purchase #5	$60.62	11.863%	$67.8114	$67.81	$67.80	$67.80
Purchase #6	$170.69	9.314%	$186.5881	$186.59	$186.60	$186.60
Purchase #7	$175.42	12.255%	$196.9177	$196.92	$196.90	$196.90
7 purchase totals =	$904.85		$998.9845	$998.98	$999.00	$998.80