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	$6.60	4.826%	$6.9185	$6.92	$6.90	$6.90
Purchase #2	$185.77	13.248%	$210.3808	$210.38	$210.40	$210.40
Purchase #3	$121.90	3.247%	$125.8581	$125.86	$125.85	$125.90
Purchase #4	$81.80	13.128%	$92.5387	$92.54	$92.55	$92.50
Purchase #5	$71.92	9.790%	$78.961	$78.96	$78.95	$79.00
Purchase #6	$82.68	3.423%	$85.5101	$85.51	$85.50	$85.50
Purchase #7	$109.31	8.721%	$118.8429	$118.84	$118.85	$118.80
7 purchase totals =	$659.98		$719.0101	$719.01	$719.00	$719.00