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	$126.43	11.643%	$141.1502	$141.15	$141.15	$141.20
Purchase #2	$231.56	12.558%	$260.6393	$260.64	$260.65	$260.60
Purchase #3	$53.99	5.553%	$56.9881	$56.99	$57.00	$57.00
Purchase #4	$97.44	12.395%	$109.5177	$109.52	$109.50	$109.50
Purchase #5	$40.82	3.577%	$42.2801	$42.28	$42.30	$42.30
Purchase #6	$92.78	8.113%	$100.3072	$100.31	$100.30	$100.30
Purchase #7	$138.38	11.352%	$154.0889	$154.09	$154.10	$154.10
7 purchase totals =	$781.40		$864.9715	$864.98	$865.00	$865.00