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	$129.40	10.207%	$142.6079	$142.61	$142.60	$142.60
Purchase #2	$85.73	11.728%	$95.7844	$95.78	$95.80	$95.80
Purchase #3	$174.83	11.504%	$194.9424	$194.94	$194.95	$194.90
Purchase #4	$70.74	11.429%	$78.8249	$78.82	$78.80	$78.80
Purchase #5	$34.46	11.187%	$38.315	$38.32	$38.30	$38.30
Purchase #6	$14.61	7.784%	$15.7472	$15.75	$15.75	$15.70
Purchase #7	$95.52	4.129%	$99.464	$99.46	$99.45	$99.50
7 purchase totals =	$605.29		$665.6858	$665.68	$665.65	$665.60