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	$99.69	12.245%	$111.897	$111.90	$111.90	$111.90
Purchase #2	$225.80	5.448%	$238.1016	$238.10	$238.10	$238.10
Purchase #3	$241.31	3.527%	$249.821	$249.82	$249.80	$249.80
Purchase #4	$83.34	11.412%	$92.8508	$92.85	$92.85	$92.90
Purchase #5	$54.39	6.706%	$58.0374	$58.04	$58.05	$58.00
Purchase #6	$88.35	4.684%	$92.4883	$92.49	$92.50	$92.50
Purchase #7	$206.47	12.603%	$232.4914	$232.49	$232.50	$232.50
7 purchase totals =	$999.35		$1,075.6875	$1,075.69	$1,075.70	$1,075.70