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	$29.48	7.621%	$31.7267	$31.73	$31.75	$31.70
Purchase #2	$240.32	3.578%	$248.9186	$248.92	$248.90	$248.90
Purchase #3	$106.92	3.870%	$111.0578	$111.06	$111.05	$111.10
Purchase #4	$46.73	11.449%	$52.0801	$52.08	$52.10	$52.10
Purchase #5	$95.67	4.583%	$100.0546	$100.05	$100.05	$100.10
Purchase #6	$114.65	4.699%	$120.0374	$120.04	$120.05	$120.00
Purchase #7	$97.79	12.393%	$109.9091	$109.91	$109.90	$109.90
7 purchase totals =	$731.56		$773.7843	$773.79	$773.80	$773.80