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	$239.31	12.536%	$269.3099	$269.31	$269.30	$269.30
Purchase #2	$78.38	6.114%	$83.1722	$83.17	$83.15	$83.20
Purchase #3	$71.50	10.335%	$78.8895	$78.89	$78.90	$78.90
Purchase #4	$185.92	6.728%	$198.4287	$198.43	$198.45	$198.40
Purchase #5	$139.60	5.368%	$147.0937	$147.09	$147.10	$147.10
Purchase #6	$34.97	9.849%	$38.4142	$38.41	$38.40	$38.40
Purchase #7	$176.81	11.609%	$197.3359	$197.34	$197.35	$197.30
7 purchase totals =	$926.49		$1,012.6441	$1,012.64	$1,012.65	$1,012.60