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	$169.84	7.497%	$182.5729	$182.57	$182.55	$182.60
Purchase #2	$124.31	10.598%	$137.4844	$137.48	$137.50	$137.50
Purchase #3	$126.99	12.508%	$142.8739	$142.87	$142.85	$142.90
Purchase #4	$78.79	13.520%	$89.4424	$89.44	$89.45	$89.40
Purchase #5	$191.43	12.324%	$215.0218	$215.02	$215.00	$215.00
Purchase #6	$48.65	8.121%	$52.6009	$52.60	$52.60	$52.60
Purchase #7	$19.89	4.196%	$20.7246	$20.72	$20.70	$20.70
7 purchase totals =	$759.90		$840.7209	$840.70	$840.65	$840.70