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	$71.49	8.288%	$77.4151	$77.42	$77.40	$77.40
Purchase #2	$127.78	5.208%	$134.4348	$134.43	$134.45	$134.40
Purchase #3	$230.81	13.337%	$261.5931	$261.59	$261.60	$261.60
Purchase #4	$37.52	13.252%	$42.4922	$42.49	$42.50	$42.50
Purchase #5	$193.72	12.552%	$218.0357	$218.04	$218.05	$218.00
Purchase #6	$41.49	5.226%	$43.6583	$43.66	$43.65	$43.70
Purchase #7	$44.61	13.275%	$50.532	$50.53	$50.55	$50.50
7 purchase totals =	$747.42		$828.1612	$828.16	$828.20	$828.10