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	$114.68	8.842%	$124.82	$124.82	$124.80	$124.80
Purchase #2	$174.94	3.682%	$181.3813	$181.38	$181.40	$181.40
Purchase #3	$137.70	7.794%	$148.4323	$148.43	$148.45	$148.40
Purchase #4	$153.50	3.474%	$158.8326	$158.83	$158.85	$158.80
Purchase #5	$152.54	6.701%	$162.7617	$162.76	$162.75	$162.80
Purchase #6	$58.94	7.803%	$63.5391	$63.54	$63.55	$63.50
Purchase #7	$73.63	6.367%	$78.318	$78.32	$78.30	$78.30
7 purchase totals =	$865.93		$918.0850	$918.08	$918.10	$918.00