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	$235.37	8.621%	$255.6612	$255.66	$255.65	$255.70
Purchase #2	$182.56	8.579%	$198.2218	$198.22	$198.20	$198.20
Purchase #3	$140.54	12.591%	$158.2354	$158.24	$158.25	$158.20
Purchase #4	$95.87	6.812%	$102.4007	$102.40	$102.40	$102.40
Purchase #5	$127.86	13.192%	$144.7273	$144.73	$144.75	$144.70
Purchase #6	$95.89	12.760%	$108.1256	$108.13	$108.15	$108.10
Purchase #7	$126.77	11.475%	$141.3169	$141.32	$141.30	$141.30
7 purchase totals =	$1,004.86		$1,108.6889	$1,108.70	$1,108.70	$1,108.60