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	$171.50	10.393%	$189.324	$189.32	$189.30	$189.30
Purchase #2	$136.31	3.608%	$141.2281	$141.23	$141.25	$141.20
Purchase #3	$137.75	5.655%	$145.5398	$145.54	$145.55	$145.50
Purchase #4	$146.98	4.260%	$153.2413	$153.24	$153.25	$153.20
Purchase #5	$242.30	5.691%	$256.0893	$256.09	$256.10	$256.10
Purchase #6	$12.94	4.323%	$13.4994	$13.50	$13.50	$13.50
Purchase #7	$50.57	3.620%	$52.4006	$52.40	$52.40	$52.40
7 purchase totals =	$898.35		$951.3225	$951.32	$951.35	$951.20