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	$249.58	11.792%	$279.0105	$279.01	$279.00	$279.00
Purchase #2	$45.72	9.637%	$50.126	$50.13	$50.15	$50.10
Purchase #3	$101.88	6.532%	$108.5348	$108.53	$108.55	$108.50
Purchase #4	$33.65	3.692%	$34.8924	$34.89	$34.90	$34.90
Purchase #5	$47.91	6.854%	$51.1938	$51.19	$51.20	$51.20
Purchase #6	$230.91	9.793%	$253.523	$253.52	$253.50	$253.50
Purchase #7	$223.52	10.307%	$246.5582	$246.56	$246.55	$246.60
7 purchase totals =	$933.17		$1,023.8387	$1,023.83	$1,023.85	$1,023.80