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	$172.63	6.539%	$183.9183	$183.92	$183.90	$183.90
Purchase #2	$196.29	13.550%	$222.8873	$222.89	$222.90	$222.90
Purchase #3	$115.83	10.749%	$128.2806	$128.28	$128.30	$128.30
Purchase #4	$37.65	5.665%	$39.7829	$39.78	$39.80	$39.80
Purchase #5	$95.27	12.866%	$107.5274	$107.53	$107.55	$107.50
Purchase #6	$184.82	10.839%	$204.8526	$204.85	$204.85	$204.90
Purchase #7	$52.62	7.562%	$56.5991	$56.60	$56.60	$56.60
7 purchase totals =	$855.11		$943.8482	$943.85	$943.90	$943.90