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	$235.91	13.396%	$267.5125	$267.51	$267.50	$267.50
Purchase #2	$248.50	12.307%	$279.0829	$279.08	$279.10	$279.10
Purchase #3	$201.68	6.517%	$214.8235	$214.82	$214.80	$214.80
Purchase #4	$153.76	12.332%	$172.7217	$172.72	$172.70	$172.70
Purchase #5	$21.27	7.408%	$22.8457	$22.85	$22.85	$22.80
Purchase #6	$182.44	9.311%	$199.427	$199.43	$199.45	$199.40
Purchase #7	$57.82	3.472%	$59.8275	$59.83	$59.85	$59.80
7 purchase totals =	$1,101.38		$1,216.2408	$1,216.24	$1,216.25	$1,216.10