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	$138.26	4.313%	$144.2232	$144.22	$144.20	$144.20
Purchase #2	$103.50	8.785%	$112.5925	$112.59	$112.60	$112.60
Purchase #3	$37.27	5.619%	$39.3642	$39.36	$39.35	$39.40
Purchase #4	$39.61	9.839%	$43.5072	$43.51	$43.50	$43.50
Purchase #5	$142.55	6.575%	$151.9227	$151.92	$151.90	$151.90
Purchase #6	$172.25	9.355%	$188.364	$188.36	$188.35	$188.40
Purchase #7	$66.75	12.337%	$74.9849	$74.98	$75.00	$75.00
7 purchase totals =	$700.19		$754.9587	$754.94	$754.90	$755.00