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	$125.75	13.636%	$142.8973	$142.90	$142.90	$142.90
Purchase #2	$139.32	11.348%	$155.13	$155.13	$155.15	$155.10
Purchase #3	$226.27	12.293%	$254.0854	$254.09	$254.10	$254.10
Purchase #4	$47.25	8.158%	$51.1047	$51.10	$51.10	$51.10
Purchase #5	$150.49	4.139%	$156.7188	$156.72	$156.70	$156.70
Purchase #6	$6.92	13.196%	$7.8332	$7.83	$7.85	$7.80
Purchase #7	$36.67	7.245%	$39.3267	$39.33	$39.35	$39.30
7 purchase totals =	$732.67		$807.0961	$807.10	$807.15	$807.00