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	$100.26	5.195%	$105.4685	$105.47	$105.45	$105.50
Purchase #2	$166.63	9.459%	$182.3915	$182.39	$182.40	$182.40
Purchase #3	$101.67	13.394%	$115.2877	$115.29	$115.30	$115.30
Purchase #4	$10.90	9.864%	$11.9752	$11.98	$12.00	$12.00
Purchase #5	$65.43	10.468%	$72.2792	$72.28	$72.30	$72.30
Purchase #6	$202.33	11.147%	$224.8837	$224.88	$224.90	$224.90
Purchase #7	$183.50	3.730%	$190.3446	$190.34	$190.35	$190.30
7 purchase totals =	$830.72		$902.6304	$902.63	$902.70	$902.70