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	$98.93	12.801%	$111.594	$111.59	$111.60	$111.60
Purchase #2	$231.86	9.770%	$254.5127	$254.51	$254.50	$254.50
Purchase #3	$93.73	9.636%	$102.7618	$102.76	$102.75	$102.80
Purchase #4	$44.48	3.473%	$46.0248	$46.02	$46.00	$46.00
Purchase #5	$63.50	8.456%	$68.8696	$68.87	$68.85	$68.90
Purchase #6	$219.62	9.434%	$240.339	$240.34	$240.35	$240.30
Purchase #7	$141.38	10.285%	$155.9209	$155.92	$155.90	$155.90
7 purchase totals =	$893.50		$980.0228	$980.01	$979.95	$980.00