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	$55.72	7.477%	$59.8862	$59.89	$59.90	$59.90
Purchase #2	$127.96	6.386%	$136.1315	$136.13	$136.15	$136.10
Purchase #3	$102.92	9.710%	$112.9135	$112.91	$112.90	$112.90
Purchase #4	$94.78	10.296%	$104.5385	$104.54	$104.55	$104.50
Purchase #5	$125.64	3.406%	$129.9193	$129.92	$129.90	$129.90
Purchase #6	$94.79	10.176%	$104.4358	$104.44	$104.45	$104.40
Purchase #7	$63.46	13.601%	$72.0912	$72.09	$72.10	$72.10
7 purchase totals =	$665.27		$719.9160	$719.92	$719.95	$719.80