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	$151.36	12.762%	$170.6766	$170.68	$170.70	$170.70
Purchase #2	$225.99	13.104%	$255.6037	$255.60	$255.60	$255.60
Purchase #3	$135.56	13.478%	$153.8308	$153.83	$153.85	$153.80
Purchase #4	$18.91	10.545%	$20.9041	$20.90	$20.90	$20.90
Purchase #5	$201.59	3.535%	$208.7162	$208.72	$208.70	$208.70
Purchase #6	$105.29	12.372%	$118.3165	$118.32	$118.30	$118.30
Purchase #7	$131.76	7.606%	$141.7817	$141.78	$141.80	$141.80
7 purchase totals =	$970.46		$1,069.8296	$1,069.83	$1,069.85	$1,069.80