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	$240.76	6.659%	$256.7922	$256.79	$256.80	$256.80
Purchase #2	$129.98	9.261%	$142.0174	$142.02	$142.00	$142.00
Purchase #3	$225.42	12.282%	$253.1061	$253.11	$253.10	$253.10
Purchase #4	$46.83	11.621%	$52.2721	$52.27	$52.25	$52.30
Purchase #5	$93.69	12.249%	$105.1661	$105.17	$105.15	$105.20
Purchase #6	$72.39	13.320%	$82.0323	$82.03	$82.05	$82.00
Purchase #7	$108.78	7.395%	$116.8243	$116.82	$116.80	$116.80
7 purchase totals =	$917.85		$1,008.2105	$1,008.21	$1,008.15	$1,008.20