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	$141.63	9.848%	$155.5777	$155.58	$155.60	$155.60
Purchase #2	$143.93	11.173%	$160.0113	$160.01	$160.00	$160.00
Purchase #3	$228.65	11.646%	$255.2786	$255.28	$255.30	$255.30
Purchase #4	$199.84	11.413%	$222.6477	$222.65	$222.65	$222.60
Purchase #5	$36.65	13.145%	$41.4676	$41.47	$41.45	$41.50
Purchase #6	$94.88	7.687%	$102.1734	$102.17	$102.15	$102.20
Purchase #7	$44.83	3.665%	$46.473	$46.47	$46.45	$46.50
7 purchase totals =	$890.41		$983.6293	$983.63	$983.60	$983.70