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	$144.38	8.813%	$157.1042	$157.10	$157.10	$157.10
Purchase #2	$230.50	11.285%	$256.5119	$256.51	$256.50	$256.50
Purchase #3	$164.98	13.376%	$187.0477	$187.05	$187.05	$187.00
Purchase #4	$78.73	8.571%	$85.4779	$85.48	$85.50	$85.50
Purchase #5	$139.91	8.247%	$151.4484	$151.45	$151.45	$151.40
Purchase #6	$117.66	5.336%	$123.9383	$123.94	$123.95	$123.90
Purchase #7	$19.30	3.854%	$20.0438	$20.04	$20.05	$20.00
7 purchase totals =	$895.46		$981.5722	$981.57	$981.60	$981.40