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	$114.73	11.684%	$128.1351	$128.14	$128.15	$128.10
Purchase #2	$90.56	12.686%	$102.0484	$102.05	$102.05	$102.00
Purchase #3	$211.67	9.172%	$231.0844	$231.08	$231.10	$231.10
Purchase #4	$183.89	4.536%	$192.2313	$192.23	$192.25	$192.20
Purchase #5	$84.36	6.191%	$89.5827	$89.58	$89.60	$89.60
Purchase #6	$115.91	13.129%	$131.1278	$131.13	$131.15	$131.10
Purchase #7	$19.89	8.466%	$21.5739	$21.57	$21.55	$21.60
7 purchase totals =	$821.01		$895.7836	$895.78	$895.85	$895.70