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	$148.94	11.848%	$166.5864	$166.59	$166.60	$166.60
Purchase #2	$123.85	5.236%	$130.3348	$130.33	$130.35	$130.30
Purchase #3	$16.89	8.526%	$18.33	$18.33	$18.35	$18.30
Purchase #4	$241.56	8.247%	$261.4815	$261.48	$261.50	$261.50
Purchase #5	$230.61	3.806%	$239.387	$239.39	$239.40	$239.40
Purchase #6	$28.38	11.747%	$31.7138	$31.71	$31.70	$31.70
Purchase #7	$115.70	13.294%	$131.0812	$131.08	$131.10	$131.10
7 purchase totals =	$905.93		$978.9147	$978.91	$979.00	$978.90