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	$154.53	3.107%	$159.3312	$159.33	$159.35	$159.30
Purchase #2	$143.61	13.393%	$162.8437	$162.84	$162.85	$162.80
Purchase #3	$211.97	6.836%	$226.4603	$226.46	$226.45	$226.50
Purchase #4	$42.45	12.109%	$47.5903	$47.59	$47.60	$47.60
Purchase #5	$31.75	4.264%	$33.1038	$33.10	$33.10	$33.10
Purchase #6	$146.40	8.492%	$158.8323	$158.83	$158.85	$158.80
Purchase #7	$129.80	12.143%	$145.5616	$145.56	$145.55	$145.60
7 purchase totals =	$860.51		$933.7232	$933.71	$933.75	$933.70