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	$24.64	11.647%	$27.5098	$27.51	$27.50	$27.50
Purchase #2	$76.75	3.235%	$79.2329	$79.23	$79.25	$79.20
Purchase #3	$219.31	13.276%	$248.4256	$248.43	$248.45	$248.40
Purchase #4	$117.43	8.856%	$127.8296	$127.83	$127.85	$127.80
Purchase #5	$127.65	12.186%	$143.2054	$143.21	$143.20	$143.20
Purchase #6	$63.25	12.592%	$71.2144	$71.21	$71.20	$71.20
Purchase #7	$70.30	8.353%	$76.1722	$76.17	$76.15	$76.20
7 purchase totals =	$699.33		$773.5899	$773.59	$773.60	$773.50