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	$213.35	9.510%	$233.6396	$233.64	$233.65	$233.60
Purchase #2	$222.83	8.406%	$241.5611	$241.56	$241.55	$241.60
Purchase #3	$174.52	10.167%	$192.2634	$192.26	$192.25	$192.30
Purchase #4	$142.67	11.154%	$158.5834	$158.58	$158.60	$158.60
Purchase #5	$40.37	8.815%	$43.9286	$43.93	$43.95	$43.90
Purchase #6	$52.46	11.725%	$58.6109	$58.61	$58.60	$58.60
Purchase #7	$65.78	8.387%	$71.297	$71.30	$71.30	$71.30
7 purchase totals =	$911.98		$999.8840	$999.88	$999.90	$999.90