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	$43.73	11.820%	$48.8989	$48.90	$48.90	$48.90
Purchase #2	$250.59	3.342%	$258.9647	$258.96	$258.95	$259.00
Purchase #3	$96.56	8.390%	$104.6614	$104.66	$104.65	$104.70
Purchase #4	$197.38	9.540%	$216.2101	$216.21	$216.20	$216.20
Purchase #5	$94.67	10.602%	$104.7069	$104.71	$104.70	$104.70
Purchase #6	$175.41	5.724%	$185.4505	$185.45	$185.45	$185.50
Purchase #7	$89.70	12.474%	$100.8892	$100.89	$100.90	$100.90
7 purchase totals =	$948.04		$1,019.7817	$1,019.78	$1,019.75	$1,019.90