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	$21.84	10.661%	$24.1684	$24.17	$24.15	$24.20
Purchase #2	$61.86	13.182%	$70.0144	$70.01	$70.00	$70.00
Purchase #3	$164.78	12.565%	$185.4846	$185.48	$185.50	$185.50
Purchase #4	$121.70	9.557%	$133.3309	$133.33	$133.35	$133.30
Purchase #5	$66.28	3.831%	$68.8192	$68.82	$68.80	$68.80
Purchase #6	$99.77	3.668%	$103.4296	$103.43	$103.45	$103.40
Purchase #7	$249.64	10.211%	$275.1307	$275.13	$275.15	$275.10
7 purchase totals =	$785.87		$860.3778	$860.37	$860.40	$860.30