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	$96.49	8.309%	$104.5074	$104.51	$104.50	$104.50
Purchase #2	$187.71	3.111%	$193.5497	$193.55	$193.55	$193.50
Purchase #3	$30.53	10.102%	$33.6141	$33.61	$33.60	$33.60
Purchase #4	$33.25	3.873%	$34.5378	$34.54	$34.55	$34.50
Purchase #5	$247.93	3.459%	$256.5059	$256.51	$256.50	$256.50
Purchase #6	$198.91	8.254%	$215.328	$215.33	$215.35	$215.30
Purchase #7	$10.34	12.721%	$11.6554	$11.66	$11.65	$11.70
7 purchase totals =	$805.16		$849.6983	$849.71	$849.70	$849.60