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	$47.41	13.724%	$53.9165	$53.92	$53.90	$53.90
Purchase #2	$103.79	7.288%	$111.3542	$111.35	$111.35	$111.40
Purchase #3	$146.79	8.350%	$159.047	$159.05	$159.05	$159.00
Purchase #4	$104.97	11.399%	$116.9355	$116.94	$116.95	$116.90
Purchase #5	$198.48	5.227%	$208.8545	$208.85	$208.85	$208.90
Purchase #6	$149.95	7.332%	$160.9443	$160.94	$160.95	$160.90
Purchase #7	$34.25	13.476%	$38.8655	$38.87	$38.85	$38.90
7 purchase totals =	$785.64		$849.9175	$849.92	$849.90	$849.90