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	$159.79	7.665%	$172.0379	$172.04	$172.05	$172.00
Purchase #2	$72.30	10.393%	$79.8141	$79.81	$79.80	$79.80
Purchase #3	$205.55	6.238%	$218.3722	$218.37	$218.35	$218.40
Purchase #4	$49.92	10.358%	$55.0907	$55.09	$55.10	$55.10
Purchase #5	$82.44	8.536%	$89.4771	$89.48	$89.50	$89.50
Purchase #6	$97.49	12.237%	$109.4199	$109.42	$109.40	$109.40
Purchase #7	$189.28	5.389%	$199.4803	$199.48	$199.50	$199.50
7 purchase totals =	$856.77		$923.6922	$923.69	$923.70	$923.70