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	$58.26	4.842%	$61.0809	$61.08	$61.10	$61.10
Purchase #2	$77.88	7.344%	$83.5995	$83.60	$83.60	$83.60
Purchase #3	$125.32	11.281%	$139.4573	$139.46	$139.45	$139.50
Purchase #4	$170.44	3.587%	$176.5537	$176.55	$176.55	$176.60
Purchase #5	$127.70	12.648%	$143.8515	$143.85	$143.85	$143.90
Purchase #6	$123.94	11.799%	$138.5637	$138.56	$138.55	$138.60
Purchase #7	$89.62	12.617%	$100.9274	$100.93	$100.95	$100.90
7 purchase totals =	$773.16		$844.0340	$844.03	$844.05	$844.20