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	$231.40	10.596%	$255.9191	$255.92	$255.90	$255.90
Purchase #2	$75.48	4.434%	$78.8268	$78.83	$78.85	$78.80
Purchase #3	$173.26	5.284%	$182.4151	$182.42	$182.40	$182.40
Purchase #4	$38.43	8.697%	$41.7723	$41.77	$41.75	$41.80
Purchase #5	$86.67	11.163%	$96.345	$96.35	$96.35	$96.30
Purchase #6	$205.58	10.438%	$227.0384	$227.04	$227.05	$227.00
Purchase #7	$34.52	11.229%	$38.3963	$38.40	$38.40	$38.40
7 purchase totals =	$845.34		$920.7130	$920.73	$920.70	$920.60