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	13.742%	$99.8314	$99.83	$99.85	$99.80
Purchase #2	$192.64	8.393%	$208.8083	$208.81	$208.80	$208.80
Purchase #3	$58.85	10.580%	$65.0763	$65.08	$65.10	$65.10
Purchase #4	$72.49	13.688%	$82.4124	$82.41	$82.40	$82.40
Purchase #5	$109.84	7.723%	$118.3229	$118.32	$118.30	$118.30
Purchase #6	$183.44	3.292%	$189.4788	$189.48	$189.50	$189.50
Purchase #7	$185.78	12.279%	$208.5919	$208.59	$208.60	$208.60
7 purchase totals =	$890.81		$972.5220	$972.52	$972.55	$972.50