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	$220.66	12.181%	$247.5386	$247.54	$247.55	$247.50
Purchase #2	$204.50	6.119%	$217.0134	$217.01	$217.00	$217.00
Purchase #3	$191.60	8.590%	$208.0584	$208.06	$208.05	$208.10
Purchase #4	$56.79	4.398%	$59.2876	$59.29	$59.30	$59.30
Purchase #5	$132.45	10.639%	$146.5414	$146.54	$146.55	$146.50
Purchase #6	$14.61	8.753%	$15.8888	$15.89	$15.90	$15.90
Purchase #7	$121.83	10.488%	$134.6075	$134.61	$134.60	$134.60
7 purchase totals =	$942.44		$1,028.9357	$1,028.94	$1,028.95	$1,028.90