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	$47.85	13.831%	$54.4681	$54.47	$54.45	$54.50
Purchase #2	$19.85	6.178%	$21.0763	$21.08	$21.10	$21.10
Purchase #3	$145.73	6.139%	$154.6764	$154.68	$154.70	$154.70
Purchase #4	$89.86	10.776%	$99.5433	$99.54	$99.55	$99.50
Purchase #5	$232.45	4.340%	$242.5383	$242.54	$242.55	$242.50
Purchase #6	$102.31	12.775%	$115.3801	$115.38	$115.40	$115.40
Purchase #7	$61.47	11.503%	$68.5409	$68.54	$68.55	$68.50
7 purchase totals =	$699.52		$756.2234	$756.23	$756.30	$756.20