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	$25.87	6.278%	$27.4941	$27.49	$27.50	$27.50
Purchase #2	$65.32	11.149%	$72.6025	$72.60	$72.60	$72.60
Purchase #3	$178.61	7.533%	$192.0647	$192.06	$192.05	$192.10
Purchase #4	$141.66	7.203%	$151.8638	$151.86	$151.85	$151.90
Purchase #5	$107.40	5.447%	$113.2501	$113.25	$113.25	$113.30
Purchase #6	$151.52	13.185%	$171.4979	$171.50	$171.50	$171.50
Purchase #7	$82.68	13.185%	$93.5814	$93.58	$93.60	$93.60
7 purchase totals =	$753.06		$822.3545	$822.34	$822.35	$822.50