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	$24.76	11.449%	$27.5948	$27.59	$27.60	$27.60
Purchase #2	$70.86	6.648%	$75.5708	$75.57	$75.55	$75.60
Purchase #3	$38.65	13.167%	$43.739	$43.74	$43.75	$43.70
Purchase #4	$92.60	11.241%	$103.0092	$103.01	$103.00	$103.00
Purchase #5	$95.37	5.162%	$100.293	$100.29	$100.30	$100.30
Purchase #6	$117.95	4.780%	$123.588	$123.59	$123.60	$123.60
Purchase #7	$87.41	13.585%	$99.2846	$99.28	$99.30	$99.30
7 purchase totals =	$527.60		$573.0794	$573.07	$573.10	$573.10