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	$65.56	10.186%	$72.2379	$72.24	$72.25	$72.20
Purchase #2	$189.37	13.287%	$214.5316	$214.53	$214.55	$214.50
Purchase #3	$58.66	3.631%	$60.7899	$60.79	$60.80	$60.80
Purchase #4	$12.95	11.209%	$14.4016	$14.40	$14.40	$14.40
Purchase #5	$191.74	9.800%	$210.5305	$210.53	$210.55	$210.50
Purchase #6	$142.35	12.737%	$160.4811	$160.48	$160.50	$160.50
Purchase #7	$81.38	11.720%	$90.9177	$90.92	$90.90	$90.90
7 purchase totals =	$742.01		$823.8903	$823.89	$823.95	$823.80