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	$16.69	6.686%	$17.8059	$17.81	$17.80	$17.80
Purchase #2	$91.49	9.425%	$100.1129	$100.11	$100.10	$100.10
Purchase #3	$218.59	6.563%	$232.9361	$232.94	$232.95	$232.90
Purchase #4	$105.62	9.856%	$116.0299	$116.03	$116.05	$116.00
Purchase #5	$161.55	10.693%	$178.8245	$178.82	$178.80	$178.80
Purchase #6	$29.54	9.317%	$32.2922	$32.29	$32.30	$32.30
Purchase #7	$76.28	8.588%	$82.8309	$82.83	$82.85	$82.80
7 purchase totals =	$699.76		$760.8324	$760.83	$760.85	$760.70