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	$100.86	10.820%	$111.7731	$111.77	$111.75	$111.80
Purchase #2	$247.90	9.134%	$270.5432	$270.54	$270.55	$270.50
Purchase #3	$152.78	5.743%	$161.5542	$161.55	$161.55	$161.60
Purchase #4	$38.40	4.413%	$40.0946	$40.09	$40.10	$40.10
Purchase #5	$17.66	7.362%	$18.9601	$18.96	$18.95	$19.00
Purchase #6	$175.71	11.545%	$195.9957	$196.00	$196.00	$196.00
Purchase #7	$172.78	8.687%	$187.7894	$187.79	$187.80	$187.80
7 purchase totals =	$906.09		$986.7103	$986.70	$986.70	$986.80