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	$66.85	12.819%	$75.4195	$75.42	$75.40	$75.40
Purchase #2	$186.98	10.108%	$205.8799	$205.88	$205.90	$205.90
Purchase #3	$112.50	3.409%	$116.3351	$116.34	$116.35	$116.30
Purchase #4	$29.82	8.414%	$32.3291	$32.33	$32.35	$32.30
Purchase #5	$154.83	11.176%	$172.1338	$172.13	$172.15	$172.10
Purchase #6	$107.77	4.412%	$112.5248	$112.52	$112.50	$112.50
Purchase #7	$218.40	3.847%	$226.8018	$226.80	$226.80	$226.80
7 purchase totals =	$877.15		$941.4240	$941.42	$941.45	$941.30