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	$108.86	3.694%	$112.8813	$112.88	$112.90	$112.90
Purchase #2	$27.27	8.541%	$29.5991	$29.60	$29.60	$29.60
Purchase #3	$133.48	8.293%	$144.5495	$144.55	$144.55	$144.50
Purchase #4	$150.85	5.304%	$158.8511	$158.85	$158.85	$158.90
Purchase #5	$65.30	9.388%	$71.4304	$71.43	$71.45	$71.40
Purchase #6	$134.96	13.329%	$152.9488	$152.95	$152.95	$152.90
Purchase #7	$221.53	3.840%	$230.0368	$230.04	$230.05	$230.00
7 purchase totals =	$842.25		$900.2970	$900.30	$900.35	$900.20