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	$60.76	11.670%	$67.8507	$67.85	$67.85	$67.90
Purchase #2	$35.74	12.351%	$40.1542	$40.15	$40.15	$40.20
Purchase #3	$64.81	8.401%	$70.2547	$70.25	$70.25	$70.30
Purchase #4	$130.68	11.276%	$145.4155	$145.42	$145.40	$145.40
Purchase #5	$116.45	6.358%	$123.8539	$123.85	$123.85	$123.90
Purchase #6	$72.88	5.426%	$76.8345	$76.83	$76.85	$76.80
Purchase #7	$43.48	9.140%	$47.4541	$47.45	$47.45	$47.50
7 purchase totals =	$524.80		$571.8176	$571.80	$571.80	$572.00