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	$87.77	13.851%	$99.927	$99.93	$99.95	$99.90
Purchase #2	$106.89	8.369%	$115.8356	$115.84	$115.85	$115.80
Purchase #3	$250.97	13.174%	$284.0328	$284.03	$284.05	$284.00
Purchase #4	$158.42	12.861%	$178.7944	$178.79	$178.80	$178.80
Purchase #5	$183.77	9.174%	$200.6291	$200.63	$200.65	$200.60
Purchase #6	$143.96	8.661%	$156.4284	$156.43	$156.45	$156.40
Purchase #7	$46.63	11.125%	$51.8176	$51.82	$51.80	$51.80
7 purchase totals =	$978.41		$1,087.4649	$1,087.47	$1,087.55	$1,087.30