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	$146.75	12.356%	$164.8824	$164.88	$164.90	$164.90
Purchase #2	$134.78	13.855%	$153.4538	$153.45	$153.45	$153.50
Purchase #3	$207.39	12.633%	$233.5896	$233.59	$233.60	$233.60
Purchase #4	$141.74	3.332%	$146.4628	$146.46	$146.45	$146.50
Purchase #5	$233.84	10.309%	$257.9466	$257.95	$257.95	$257.90
Purchase #6	$22.25	13.312%	$25.2119	$25.21	$25.20	$25.20
Purchase #7	$145.52	8.776%	$158.2908	$158.29	$158.30	$158.30
7 purchase totals =	$1,032.27		$1,139.8379	$1,139.83	$1,139.85	$1,139.90