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	$224.71	9.217%	$245.4215	$245.42	$245.40	$245.40
Purchase #2	$111.88	10.676%	$123.8243	$123.82	$123.80	$123.80
Purchase #3	$15.97	10.850%	$17.7027	$17.70	$17.70	$17.70
Purchase #4	$9.43	10.776%	$10.4462	$10.45	$10.45	$10.40
Purchase #5	$214.38	3.785%	$222.4943	$222.49	$222.50	$222.50
Purchase #6	$69.69	13.139%	$78.8466	$78.85	$78.85	$78.80
Purchase #7	$12.38	6.789%	$13.2205	$13.22	$13.20	$13.20
7 purchase totals =	$658.44		$711.9561	$711.95	$711.90	$711.80