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	$24.91	9.766%	$27.3427	$27.34	$27.35	$27.30
Purchase #2	$206.52	3.666%	$214.091	$214.09	$214.10	$214.10
Purchase #3	$138.80	11.671%	$154.9993	$155.00	$155.00	$155.00
Purchase #4	$111.68	10.426%	$123.3238	$123.32	$123.30	$123.30
Purchase #5	$147.54	7.504%	$158.6114	$158.61	$158.60	$158.60
Purchase #6	$19.90	4.862%	$20.8675	$20.87	$20.85	$20.90
Purchase #7	$242.30	5.807%	$256.3704	$256.37	$256.35	$256.40
7 purchase totals =	$891.65		$955.6061	$955.60	$955.55	$955.60