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	$234.71	10.578%	$259.5376	$259.54	$259.55	$259.50
Purchase #2	$103.75	12.635%	$116.8588	$116.86	$116.85	$116.90
Purchase #3	$163.52	13.361%	$185.3679	$185.37	$185.35	$185.40
Purchase #4	$127.47	13.288%	$144.4082	$144.41	$144.40	$144.40
Purchase #5	$194.82	6.514%	$207.5106	$207.51	$207.50	$207.50
Purchase #6	$97.37	8.537%	$105.6825	$105.68	$105.70	$105.70
Purchase #7	$237.39	12.536%	$267.1492	$267.15	$267.15	$267.10
7 purchase totals =	$1,159.03		$1,286.5148	$1,286.52	$1,286.50	$1,286.50