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	$93.44	5.762%	$98.824	$98.82	$98.80	$98.80
Purchase #2	$95.30	10.712%	$105.5085	$105.51	$105.50	$105.50
Purchase #3	$235.81	7.446%	$253.3684	$253.37	$253.35	$253.40
Purchase #4	$105.42	8.638%	$114.5262	$114.53	$114.55	$114.50
Purchase #5	$73.98	6.861%	$79.0558	$79.06	$79.05	$79.10
Purchase #6	$161.73	4.348%	$168.762	$168.76	$168.75	$168.80
Purchase #7	$131.88	5.798%	$139.5264	$139.53	$139.55	$139.50
7 purchase totals =	$897.56		$959.5713	$959.58	$959.55	$959.60