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	$17.60	7.547%	$18.9283	$18.93	$18.95	$18.90
Purchase #2	$171.76	4.682%	$179.8018	$179.80	$179.80	$179.80
Purchase #3	$83.48	10.798%	$92.4942	$92.49	$92.50	$92.50
Purchase #4	$164.98	8.547%	$179.0808	$179.08	$179.10	$179.10
Purchase #5	$30.95	4.833%	$32.4458	$32.45	$32.45	$32.40
Purchase #6	$113.63	9.329%	$124.2305	$124.23	$124.25	$124.20
Purchase #7	$37.76	13.488%	$42.8531	$42.85	$42.85	$42.90
7 purchase totals =	$620.16		$669.8345	$669.83	$669.90	$669.80